CA1214943A - Recovery of metal values from a pulp containing such values in dissolved form - Google Patents
Recovery of metal values from a pulp containing such values in dissolved formInfo
- Publication number
- CA1214943A CA1214943A CA000442399A CA442399A CA1214943A CA 1214943 A CA1214943 A CA 1214943A CA 000442399 A CA000442399 A CA 000442399A CA 442399 A CA442399 A CA 442399A CA 1214943 A CA1214943 A CA 1214943A
- Authority
- CA
- Canada
- Prior art keywords
- column
- particles
- pulp
- bed
- values
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000002184 metal Substances 0.000 title claims abstract description 28
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 28
- 238000011084 recovery Methods 0.000 title claims description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 63
- 239000002245 particle Substances 0.000 claims abstract description 54
- 238000000034 method Methods 0.000 claims abstract description 49
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims abstract description 28
- 229910052737 gold Inorganic materials 0.000 claims abstract description 28
- 239000010931 gold Substances 0.000 claims abstract description 28
- 239000000463 material Substances 0.000 claims abstract description 9
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052709 silver Inorganic materials 0.000 claims abstract description 8
- 239000004332 silver Substances 0.000 claims abstract description 8
- 239000007787 solid Substances 0.000 claims description 16
- 239000003456 ion exchange resin Substances 0.000 claims description 5
- 229920003303 ion-exchange polymer Polymers 0.000 claims description 5
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 claims description 3
- 229920001429 chelating resin Polymers 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 description 26
- 238000011068 loading method Methods 0.000 description 8
- 241000196324 Embryophyta Species 0.000 description 5
- 238000000926 separation method Methods 0.000 description 5
- 238000012360 testing method Methods 0.000 description 4
- 239000003463 adsorbent Substances 0.000 description 3
- 238000005065 mining Methods 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- XFXPMWWXUTWYJX-UHFFFAOYSA-N Cyanide Chemical compound N#[C-] XFXPMWWXUTWYJX-UHFFFAOYSA-N 0.000 description 2
- 229920002522 Wood fibre Polymers 0.000 description 2
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 230000002045 lasting effect Effects 0.000 description 2
- 238000002386 leaching Methods 0.000 description 2
- 238000012216 screening Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 235000013162 Cocos nucifera Nutrition 0.000 description 1
- 244000060011 Cocos nucifera Species 0.000 description 1
- 238000013019 agitation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000005119 centrifugation Methods 0.000 description 1
- 238000009388 chemical precipitation Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000010908 decantation Methods 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000005363 electrowinning Methods 0.000 description 1
- 238000010828 elution Methods 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000003921 particle size analysis Methods 0.000 description 1
- MNWBNISUBARLIT-UHFFFAOYSA-N sodium cyanide Chemical compound [Na+].N#[C-] MNWBNISUBARLIT-UHFFFAOYSA-N 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B11/00—Obtaining noble metals
- C22B11/04—Obtaining noble metals by wet processes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Manufacturing & Machinery (AREA)
- Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Treatment Of Liquids With Adsorbents In General (AREA)
- Water Treatment By Sorption (AREA)
Abstract
ABSTRACT
A method of recovering metal values,e.g. gold and silver values from a pulp containing such metal values in dissolved form includes the steps of forming a bed comprising a randon mass of particles of a material such as activated carbon which is capable of removing the metal values from the pulp, in a column having a feed end and a discharge end, and passing a stream of the pulp through the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially stationary non-fluidised state between the feed end and the discharge end.The stream of pulp is periodically stopped so that the particles of the bed move back toward the feed end of the column.
A method of recovering metal values,e.g. gold and silver values from a pulp containing such metal values in dissolved form includes the steps of forming a bed comprising a randon mass of particles of a material such as activated carbon which is capable of removing the metal values from the pulp, in a column having a feed end and a discharge end, and passing a stream of the pulp through the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially stationary non-fluidised state between the feed end and the discharge end.The stream of pulp is periodically stopped so that the particles of the bed move back toward the feed end of the column.
Description
BACKGROUND OF THE INVENTION
This invention relates to the recovery of metal values from a pulp containing such values in dissolved form.
In mining operations, the mined ore is generally crushed and milled 5 and is then subjected to a leaching step with a suitable chemical reagent in order to solubilise the metal values of interest in the ore, the resultant product being called a pulp. Such a pulp may contain from about 1 to about 60 percent by weight solids, but typically contains 30 to 50 percent be weight solids. Such pulps 10 are commonly subjected to a liquid-solid separation stage prior to the recovery of the metal values from the resulting clarified or partially clari~ied solution. Typically such a liquid-solid separation stage may take the form of thickening, followed by filtration. Cycloning, centrifugation and counter-current lS decantation may also be used in such a liquid-solid separation stage.
Prior art methods of dealing with this clarified or partially clarified solution resulting from a liquid-solid separation stage as described above, cover a wide spectrum of metallurgical routes.
Thus, for example, the use of ion exchange resins and solvents, 5 adsorbents such as activated carbon, together with the chemical precipitation and electrowinning of rnetal values, are conventional techniques well known in the art of metal recovery.
Ihe pulp may also be treated with ion exchange resins or adsorbents such as activated carbon in the so-called "in-pulp" processes, in 10 which no prior liquid solid separation is carried out. One of the most successful methods currently being used is the carbon-in-pulp process for the recovery of gold and silver values. This method involves contacting the pulp with granular activated carbon. The gold and other valuable rnetal values are adsorbed on to the 15 activated carbon from whence they may be recovered by a variety of known techniques. This method is usually carried out by contacting the leached pulp with the activated carbon in a counter-curren-t fashion involving a series of contacting stages. In each stage the activated carbon is agitated in the leached pulp in a suitable 20 vessel. Average pulp residence times in the process are commonly in the region of four to eight hours while average carbon residence times may be ten to thirty days. A high degree of interstage carbon mixing is common to the process by virtue of the methods used in transferring carbon from one stage to another. This carbon 25 mixing has a detrimental effect on the metallurgical efficiency of the process.
While the carbon-in-pulp process achieves excellent recoveries of gold and silver values, it requires large contacting vessels and is energy intensive. The large contacting vessels are required 30 because low carbon concentrations are used to minimise mechanical problems, e.g. inter-stage screening and breakdown of the carbon.
As -the adsorption of gold and silver are critically affected by the carbon concentration, relatively 510w carbon and pulp movement rates are common to the process. Such slow movement rates result in low gold loadings on the carbon going forward to the elution circuit as well as a high degree of metal value lock-up in the adsorption circuit. This lock-up of metal values in a carbon-in-pulp circuit may constitute a major indirect opera-ting cost due to the value of the contained metals. Further, -the inters-tage screen-ing of carbon at each contacting stage of -the process may also present a major mechanical problem particularly on large plants where relative screen areas are limited due to the large size of the contacting vessels.
SUMMARY OF THE_ NVENTION
According to the present invention, there is provided a method of recovering metal values selected from gold and silver values from a pulp containing such values in dissolved form includes the steps of:
(a) forming a bed comprising a random mass of particles of a ~0 material capable of removing the metal values from the pulp selected from an ion exchange resin, a chelating resin and acti-vated carbon, in a column having a feed end and a discharge end, and (b) passing a stream of the pulp through -the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially s-tationary non fluidised state between the feed end and the discharge end of the colurnn.
DETAILED DESCRIPTION OF THE INVENlION
.. .... _ _ The method of the invention will now be described in more detail.
Initially the particles in the bed are at rest. Once the s-tream of the pulp begins to be passed through the bed, the particles move 5 towards the discharge end of the column and become suspended in a substantially stationary non-fluidised state between the feed end and the discharge end of the column. As the stream of the pulp passes through the bed, the metal values in the pulp are captured by the particles, and a concentration or loading gradient is 10 established in the bed, with the particles closest to the feed end having higher metal value loadings than the particles near the discharge end. It is important that this ccncentration gradient be maintained in the bed so that periodically, the particles having the highest metal value loadings, may be removed from the bed, and 15 replaced by fresh particles. This is achieved by ensuring that the particles are suspended in a substantially stationary non-fluidised - state so that there is no mixing or agitation of the particles in the bed.
The column for use in the method of the invention is preferably 20 inclined upwardly, with the feed end being below the discharge end, and more preferably, the column is substantially vertical. In this case, the stream of the pulp will be passed in an up-flow mode through the bed. The bed of the particles may be confined within the column by means of suitable screens which will allow the flow of 25 pulp therethrough, but which will prevent the passage of the particles therethrough. When there is an upward flow of the pulp through the bed, the flow velocity and the viscosity of the pulp will generally be sufficient to lift and suspend the particles oF
the bed in a substantially stationary non-fluidised state.
The method of the invention preferably includes the step of periodically stopping the passing of the stream of the pulp through the column so that the particles of the bed move back towards the feed end of the column while remaining in a substantially non-5 fluidised state. This relaxation of the bed reduces any tendencyfor clogging or choking of the bed to occur.
The method of the invention preferably also includes the step of periodically removing the particles in a selected zone of the bed from the column. Preferably, the particles having the highest 10 metal value loadings, i.e. the particles in -the zone nearest the feed end of the column, are removed from the bed. The removed particles may then be further treated to recover the metal values therefrom.
Generally these removed particles will be replaced with a similar 15 volume of fresh particles introduced into the column from the discharge end of the column.
The method of the invention may be applied to a plurality of beds in which each bed is discrete, or in which the beds form part of a continuous bed. Under normal operation, the passage of the pulp 20 through the system is counter-current to that of the particles of the material forming the bed in order to maximise metallurgical efficiency. The movement of the particles of the bed in such an operation may be carried out either continuously or intermittently.
The material capable of removing the metal values from the pulp may 25 be a suitable ion exchange resin, a suitable chelating resin, or an adsorbent such as activated carbon.
:~2~ 3 ~ 7 -The rate of adsorption of metal values from solution must be such that the inventory of particles and the loading of metal values on the particles are within acceptable limits. Generally this implies the use of relatively small particles which have a relatively large 5 surface area per unit volume.
Further, the particles of the material must be of a size and shape as to allow for the passage of the pulp through the bed of the particles. Thus, the particles may be elongate in shape and may be solid or may have an elongate hole extending partially or wholly 10 therethrough. For example, when the material is activated carbon, the particles may comprise rod-like pieces having a substantially circular cross-section, with a diameter of 2 to 5 mm, which are made by an extrusion process. However, other shapes and sizes of particles are also suitable for the method of the invention, e.g.
15 irregular shaped pieces with a maximum dimension of 2 to 20 mm.
Essential to the method of the invention is that the metal values are recovered from a pulp and not a clarified solution~ The pulp, which may be formed by leaching a crushed and milled ore with a suitable chemical reagent, will generally have a solids content of 20 10 to ~0 percent by weight, more typically 30 to 50 percent by weight. The solids in such pulps are usually in fine particulate form, e.g. having a typical particle size of less than 300 microns.
The method of the invention has particular application to the recovery of gold and silver values from a pulp containing such 25 values in dissolved form. In this case, it is preferred to use particles of activated carbon in the bed.
~xamples illustrating the method of the invention will now be given.
/
This example illustrates the treatment of a gold plant residue pulp taken from the President ~teyn Gold Mine according to the method of 5 the invention.
The pulp, resulting from a conventional gold leach operation, contained approximately 48 percent by weight solids. Approximately 80 percent of the solids had a particle size of less than 74 microns. As a considerable quantity of wood fibre was present in 10 the pulp, this was screened off using a 425 micron vibrating screen prior to use. The pulp was contained in a 200 litre vessel fitted with a suitable stirrer from where it was circulated through a vertical column. lhe column was 2 metres long and had an internal diameter of 200 mm. A wedge wire screen with a 2 mm slit gap was 15 positioned at the top of the column in order to confine the bed in the column. Approximately 30 kg of calcined coconut shell activated carbon, pre-screened to 3 to 15 mm in si7e, was contained in the column, leaving a freeboard depth of about 15 mm. The pulp was circulated through the column at a flow rate of 15 to 20 litres 20 per minute. The gauge pressure drop across the column during this operation measured 80 to 90 kilopascals. No choking of the column with coarse sol1ds was indicated following continuous operation lasting five hours.
~ = ~ . v 25 This example illustrates the treatment of a gold plant residue pulp similar to that used in Example 1 according to the method of the invention.
~L2-~4~3 The same column as used in Example 1 was used again, but the column contained approximately 30 kilograms of extruded activated carbon.
The extruded activated carbon was tube-like in shape having a diameter of 3 mm with particle sizes varying from 5 to 15 mrn long.
5 The leached pulp was contained in a 200 litre vessel fitted with a suitable stirrer from where it was circulated through the column a-t a flow rate of 30 litres per minute. The gauge pressure drop -across the column during this operation measured 80 kilopascals.
No choking of the column with coarse solids was indicated following 10 continuous operation lasting several days.
This example illustrates the gold recovery obtainable utilising the method of the invention.
Leached pulp containing 6 to 11 milligrams per litre of gold in 15 solution was taken from the existing gold plant circuit at the Vaal Reefs Exploration and Mining Company (South Division) and pumped in an up-flow mode into a column containing activated carbon. The pulp resulting from a conventional gold leach using cyanide, contained approximately 40 to 50 percent solids by weight having an 20 average particle size analysis as follows: 2,5 percent + 150 microns; 26,4 percent + 74 microns and 71,1 percent - 74 microns.
The leached pulp also contained approximately 200 milligrams per litre cyanide as NaCN, and had a pH in the range 10 to 11,5. A
considerable quantity of wood fibre was also present in the pulp and 25 this was screened off using a 425 micron vibrating screen prior to use. The column was 10 metres long and had an internal diameter o~
185 mm. A wedge wire screen with a 2 mm slit gap was positioned at the top of the column in order to confine the activated carbon in the column. Approximately 150 kilograms of 3 mm diameter extruded 30 or molded activated carbon was contained in the column leaving a free-board bed depth of about 300 mm. The pulp was pumped into the column a-t a flow rate of 15 litres per minute which corresponded to a superficial flow velocity in the column of 0,56 metre per minute.
The counter-current movement of carbon in the column was carried out 5 on an eight hour shift basis. Loaded carbon was discharged from the bottom of the column, while a similar volume of virgin carbon was added to the top of the column. During normal column operation the line pressure to the column averaged 300 to 500 kilopascals (gauge pressure). The counter-current movement of carbon as 10 described above nad a most beneficial effect on reducing the line pressure to the column.
The column was run in the mode described for a period of 32 days with operational time including carbon movement approaching 97 percent. During this time the recovery of soluble gold in the pulp 15 averaged 99 percent with the soluble feed to the column averaging 9,6 milligrams per litre of gold. When carbon was moved at a rate corresponding in volume to a bed depth of one third of a metre per eight hour shift, loaded carbon from the column contained 10 to 11 kilograms of gold per tonne of carbon. Likewise, when carbon was 20 moved at twice this rate, the loaded carbon contained approximately 5 kilograms of gold per tonne of carbon.
.., Residue pulp containing 0,1 to 0,4 milligrams per litre of gold in solution was taken from the existing gold plant circuit at the Vaal 25 Reefs Exploration and Mining Company ~South Division) and pumped into a column as described in Example 3.
In the first test of 9 days duration, using a 10 metre long column, the gold in solution was reduced to 0,001 milligrams per litre. In a second test of 15 days duration, where the column was shortened to 5 metres, the gold in solution was reduced to 0,005 milligrams per 5 litre. The respective gold recoveries were 99 percent and 95 percent. The pulp conditions in both these tests were similar to those described in Example 3. Duriny normal operation on the 5 metre column, the line pressure to the column averaged 100 to 200 kilopascals (gauge pressure). In both tests the carbon movement 10 rate was maintained at one third of a metre per 8 hour shift. The carbon removed was loaded with 150 to 200 grammes of gold per tonne of carbon. Any reduction in the carbon movement rate would result in higher gold loadings on the carbon.
The method of the invention has several advantages. Firstly, using 15 the method of the invention, much lower pulp residence times in the column are obtainable, when compared with the carbon-in-pulp me+hod.
For example, pulp residence times for the method of the invention are a matter of minutes compared with residence times of several hours for the conventional carbon-in-pulp method. Secondly, it is 20 possible to obtain higher metal value loadings on the metal-capturing particles.
This invention relates to the recovery of metal values from a pulp containing such values in dissolved form.
In mining operations, the mined ore is generally crushed and milled 5 and is then subjected to a leaching step with a suitable chemical reagent in order to solubilise the metal values of interest in the ore, the resultant product being called a pulp. Such a pulp may contain from about 1 to about 60 percent by weight solids, but typically contains 30 to 50 percent be weight solids. Such pulps 10 are commonly subjected to a liquid-solid separation stage prior to the recovery of the metal values from the resulting clarified or partially clari~ied solution. Typically such a liquid-solid separation stage may take the form of thickening, followed by filtration. Cycloning, centrifugation and counter-current lS decantation may also be used in such a liquid-solid separation stage.
Prior art methods of dealing with this clarified or partially clarified solution resulting from a liquid-solid separation stage as described above, cover a wide spectrum of metallurgical routes.
Thus, for example, the use of ion exchange resins and solvents, 5 adsorbents such as activated carbon, together with the chemical precipitation and electrowinning of rnetal values, are conventional techniques well known in the art of metal recovery.
Ihe pulp may also be treated with ion exchange resins or adsorbents such as activated carbon in the so-called "in-pulp" processes, in 10 which no prior liquid solid separation is carried out. One of the most successful methods currently being used is the carbon-in-pulp process for the recovery of gold and silver values. This method involves contacting the pulp with granular activated carbon. The gold and other valuable rnetal values are adsorbed on to the 15 activated carbon from whence they may be recovered by a variety of known techniques. This method is usually carried out by contacting the leached pulp with the activated carbon in a counter-curren-t fashion involving a series of contacting stages. In each stage the activated carbon is agitated in the leached pulp in a suitable 20 vessel. Average pulp residence times in the process are commonly in the region of four to eight hours while average carbon residence times may be ten to thirty days. A high degree of interstage carbon mixing is common to the process by virtue of the methods used in transferring carbon from one stage to another. This carbon 25 mixing has a detrimental effect on the metallurgical efficiency of the process.
While the carbon-in-pulp process achieves excellent recoveries of gold and silver values, it requires large contacting vessels and is energy intensive. The large contacting vessels are required 30 because low carbon concentrations are used to minimise mechanical problems, e.g. inter-stage screening and breakdown of the carbon.
As -the adsorption of gold and silver are critically affected by the carbon concentration, relatively 510w carbon and pulp movement rates are common to the process. Such slow movement rates result in low gold loadings on the carbon going forward to the elution circuit as well as a high degree of metal value lock-up in the adsorption circuit. This lock-up of metal values in a carbon-in-pulp circuit may constitute a major indirect opera-ting cost due to the value of the contained metals. Further, -the inters-tage screen-ing of carbon at each contacting stage of -the process may also present a major mechanical problem particularly on large plants where relative screen areas are limited due to the large size of the contacting vessels.
SUMMARY OF THE_ NVENTION
According to the present invention, there is provided a method of recovering metal values selected from gold and silver values from a pulp containing such values in dissolved form includes the steps of:
(a) forming a bed comprising a random mass of particles of a ~0 material capable of removing the metal values from the pulp selected from an ion exchange resin, a chelating resin and acti-vated carbon, in a column having a feed end and a discharge end, and (b) passing a stream of the pulp through -the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially s-tationary non fluidised state between the feed end and the discharge end of the colurnn.
DETAILED DESCRIPTION OF THE INVENlION
.. .... _ _ The method of the invention will now be described in more detail.
Initially the particles in the bed are at rest. Once the s-tream of the pulp begins to be passed through the bed, the particles move 5 towards the discharge end of the column and become suspended in a substantially stationary non-fluidised state between the feed end and the discharge end of the column. As the stream of the pulp passes through the bed, the metal values in the pulp are captured by the particles, and a concentration or loading gradient is 10 established in the bed, with the particles closest to the feed end having higher metal value loadings than the particles near the discharge end. It is important that this ccncentration gradient be maintained in the bed so that periodically, the particles having the highest metal value loadings, may be removed from the bed, and 15 replaced by fresh particles. This is achieved by ensuring that the particles are suspended in a substantially stationary non-fluidised - state so that there is no mixing or agitation of the particles in the bed.
The column for use in the method of the invention is preferably 20 inclined upwardly, with the feed end being below the discharge end, and more preferably, the column is substantially vertical. In this case, the stream of the pulp will be passed in an up-flow mode through the bed. The bed of the particles may be confined within the column by means of suitable screens which will allow the flow of 25 pulp therethrough, but which will prevent the passage of the particles therethrough. When there is an upward flow of the pulp through the bed, the flow velocity and the viscosity of the pulp will generally be sufficient to lift and suspend the particles oF
the bed in a substantially stationary non-fluidised state.
The method of the invention preferably includes the step of periodically stopping the passing of the stream of the pulp through the column so that the particles of the bed move back towards the feed end of the column while remaining in a substantially non-5 fluidised state. This relaxation of the bed reduces any tendencyfor clogging or choking of the bed to occur.
The method of the invention preferably also includes the step of periodically removing the particles in a selected zone of the bed from the column. Preferably, the particles having the highest 10 metal value loadings, i.e. the particles in -the zone nearest the feed end of the column, are removed from the bed. The removed particles may then be further treated to recover the metal values therefrom.
Generally these removed particles will be replaced with a similar 15 volume of fresh particles introduced into the column from the discharge end of the column.
The method of the invention may be applied to a plurality of beds in which each bed is discrete, or in which the beds form part of a continuous bed. Under normal operation, the passage of the pulp 20 through the system is counter-current to that of the particles of the material forming the bed in order to maximise metallurgical efficiency. The movement of the particles of the bed in such an operation may be carried out either continuously or intermittently.
The material capable of removing the metal values from the pulp may 25 be a suitable ion exchange resin, a suitable chelating resin, or an adsorbent such as activated carbon.
:~2~ 3 ~ 7 -The rate of adsorption of metal values from solution must be such that the inventory of particles and the loading of metal values on the particles are within acceptable limits. Generally this implies the use of relatively small particles which have a relatively large 5 surface area per unit volume.
Further, the particles of the material must be of a size and shape as to allow for the passage of the pulp through the bed of the particles. Thus, the particles may be elongate in shape and may be solid or may have an elongate hole extending partially or wholly 10 therethrough. For example, when the material is activated carbon, the particles may comprise rod-like pieces having a substantially circular cross-section, with a diameter of 2 to 5 mm, which are made by an extrusion process. However, other shapes and sizes of particles are also suitable for the method of the invention, e.g.
15 irregular shaped pieces with a maximum dimension of 2 to 20 mm.
Essential to the method of the invention is that the metal values are recovered from a pulp and not a clarified solution~ The pulp, which may be formed by leaching a crushed and milled ore with a suitable chemical reagent, will generally have a solids content of 20 10 to ~0 percent by weight, more typically 30 to 50 percent by weight. The solids in such pulps are usually in fine particulate form, e.g. having a typical particle size of less than 300 microns.
The method of the invention has particular application to the recovery of gold and silver values from a pulp containing such 25 values in dissolved form. In this case, it is preferred to use particles of activated carbon in the bed.
~xamples illustrating the method of the invention will now be given.
/
This example illustrates the treatment of a gold plant residue pulp taken from the President ~teyn Gold Mine according to the method of 5 the invention.
The pulp, resulting from a conventional gold leach operation, contained approximately 48 percent by weight solids. Approximately 80 percent of the solids had a particle size of less than 74 microns. As a considerable quantity of wood fibre was present in 10 the pulp, this was screened off using a 425 micron vibrating screen prior to use. The pulp was contained in a 200 litre vessel fitted with a suitable stirrer from where it was circulated through a vertical column. lhe column was 2 metres long and had an internal diameter of 200 mm. A wedge wire screen with a 2 mm slit gap was 15 positioned at the top of the column in order to confine the bed in the column. Approximately 30 kg of calcined coconut shell activated carbon, pre-screened to 3 to 15 mm in si7e, was contained in the column, leaving a freeboard depth of about 15 mm. The pulp was circulated through the column at a flow rate of 15 to 20 litres 20 per minute. The gauge pressure drop across the column during this operation measured 80 to 90 kilopascals. No choking of the column with coarse sol1ds was indicated following continuous operation lasting five hours.
~ = ~ . v 25 This example illustrates the treatment of a gold plant residue pulp similar to that used in Example 1 according to the method of the invention.
~L2-~4~3 The same column as used in Example 1 was used again, but the column contained approximately 30 kilograms of extruded activated carbon.
The extruded activated carbon was tube-like in shape having a diameter of 3 mm with particle sizes varying from 5 to 15 mrn long.
5 The leached pulp was contained in a 200 litre vessel fitted with a suitable stirrer from where it was circulated through the column a-t a flow rate of 30 litres per minute. The gauge pressure drop -across the column during this operation measured 80 kilopascals.
No choking of the column with coarse solids was indicated following 10 continuous operation lasting several days.
This example illustrates the gold recovery obtainable utilising the method of the invention.
Leached pulp containing 6 to 11 milligrams per litre of gold in 15 solution was taken from the existing gold plant circuit at the Vaal Reefs Exploration and Mining Company (South Division) and pumped in an up-flow mode into a column containing activated carbon. The pulp resulting from a conventional gold leach using cyanide, contained approximately 40 to 50 percent solids by weight having an 20 average particle size analysis as follows: 2,5 percent + 150 microns; 26,4 percent + 74 microns and 71,1 percent - 74 microns.
The leached pulp also contained approximately 200 milligrams per litre cyanide as NaCN, and had a pH in the range 10 to 11,5. A
considerable quantity of wood fibre was also present in the pulp and 25 this was screened off using a 425 micron vibrating screen prior to use. The column was 10 metres long and had an internal diameter o~
185 mm. A wedge wire screen with a 2 mm slit gap was positioned at the top of the column in order to confine the activated carbon in the column. Approximately 150 kilograms of 3 mm diameter extruded 30 or molded activated carbon was contained in the column leaving a free-board bed depth of about 300 mm. The pulp was pumped into the column a-t a flow rate of 15 litres per minute which corresponded to a superficial flow velocity in the column of 0,56 metre per minute.
The counter-current movement of carbon in the column was carried out 5 on an eight hour shift basis. Loaded carbon was discharged from the bottom of the column, while a similar volume of virgin carbon was added to the top of the column. During normal column operation the line pressure to the column averaged 300 to 500 kilopascals (gauge pressure). The counter-current movement of carbon as 10 described above nad a most beneficial effect on reducing the line pressure to the column.
The column was run in the mode described for a period of 32 days with operational time including carbon movement approaching 97 percent. During this time the recovery of soluble gold in the pulp 15 averaged 99 percent with the soluble feed to the column averaging 9,6 milligrams per litre of gold. When carbon was moved at a rate corresponding in volume to a bed depth of one third of a metre per eight hour shift, loaded carbon from the column contained 10 to 11 kilograms of gold per tonne of carbon. Likewise, when carbon was 20 moved at twice this rate, the loaded carbon contained approximately 5 kilograms of gold per tonne of carbon.
.., Residue pulp containing 0,1 to 0,4 milligrams per litre of gold in solution was taken from the existing gold plant circuit at the Vaal 25 Reefs Exploration and Mining Company ~South Division) and pumped into a column as described in Example 3.
In the first test of 9 days duration, using a 10 metre long column, the gold in solution was reduced to 0,001 milligrams per litre. In a second test of 15 days duration, where the column was shortened to 5 metres, the gold in solution was reduced to 0,005 milligrams per 5 litre. The respective gold recoveries were 99 percent and 95 percent. The pulp conditions in both these tests were similar to those described in Example 3. Duriny normal operation on the 5 metre column, the line pressure to the column averaged 100 to 200 kilopascals (gauge pressure). In both tests the carbon movement 10 rate was maintained at one third of a metre per 8 hour shift. The carbon removed was loaded with 150 to 200 grammes of gold per tonne of carbon. Any reduction in the carbon movement rate would result in higher gold loadings on the carbon.
The method of the invention has several advantages. Firstly, using 15 the method of the invention, much lower pulp residence times in the column are obtainable, when compared with the carbon-in-pulp me+hod.
For example, pulp residence times for the method of the invention are a matter of minutes compared with residence times of several hours for the conventional carbon-in-pulp method. Secondly, it is 20 possible to obtain higher metal value loadings on the metal-capturing particles.
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of recovering metal values selected from gold and silver values from a pulp containing such values in dissolved form includes the steps of:
(a) forming a bed comprising a random mass of particles of a material capable of removing the metal values from the pulp selected from an ion exchange resin, a chelating resin and acti-vated carbon, in a column having a feed end and a discharge end, and (b) passing a stream of the pulp through the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially stationary non fluidised state between the feed end and the discharge end of the column.
(a) forming a bed comprising a random mass of particles of a material capable of removing the metal values from the pulp selected from an ion exchange resin, a chelating resin and acti-vated carbon, in a column having a feed end and a discharge end, and (b) passing a stream of the pulp through the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially stationary non fluidised state between the feed end and the discharge end of the column.
2. A method according to claim 1 wherein the column is upwardly inclined, with the feed end being below the discharge end.
3. A method according to claim 2 wherein the column is substan-tially vertical.
4. A method according to claim 1 which includes the step of periodically stopping the passing of the stream of the pulp through the column so that the particles of the bed move back toward the feed end of the column while remaining in a substantially non-fluidised state.
5. A method according to claim 1 which includes the step of periodically removing the particles in a selected zone of the bed from the column.
6. A method according to claim 5 wherein the particles in the zone of the bed nearest the feed end of the column are removed from the bed.
7. A method according to claim 6 wherein the particles removed from the bed are replaced with a similar volume of particles introduced into the column from the discharge end of the column.
8. A method according to claim 1 wherein the particles have a relatively large surface area per unit volume.
9. A method according to claim 1 wherein the material capable of removing the metal values from the pulp comprises activated carbon.
10. A method according to claim 1 or 9 wherein the particles are elongate in shape.
11. A method according to claim 1 wherein the pulp has a solids content of 10 to 60 percent by weight.
12. A method according to claim 11 wherein the pulp has a solids content of 30 to 50 percent by weight.
13. A method of recovering metal values from a pulp containing such values in dissolved form includes the steps of:
(a) forming a bed comprising a random mass of particles of a material capable of removing the metal value from the pulp, in a column having a feed end and a discharge end;
(b) passing a stream of the pulp through the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially stationary non-fluidised state between the feed end and the discharge end of the column;
(c) periodically stopping the passing of the stream of the pulp through the column so that the particles of the bed move towards the feed end of the column while remaining in a substantially non-fluidised state; and (d) periodically removing the particles in a selected zone of the bed from the column.
(a) forming a bed comprising a random mass of particles of a material capable of removing the metal value from the pulp, in a column having a feed end and a discharge end;
(b) passing a stream of the pulp through the column from the feed end to the discharge end so that the particles of the bed are suspended in a substantially stationary non-fluidised state between the feed end and the discharge end of the column;
(c) periodically stopping the passing of the stream of the pulp through the column so that the particles of the bed move towards the feed end of the column while remaining in a substantially non-fluidised state; and (d) periodically removing the particles in a selected zone of the bed from the column.
14. A method according to claim 13 wherein the column is sub-stantially vertical.
15. A method according to claim 13 or claim 14 which includes the step of replacing the particles removed from the bed with a similar volume of particles introduced into the column from the discharge end of the column.
16. A method according to claim 13 for the recovery of gold and silver values from a pulp containing such values in dissolved form.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA828866 | 1982-12-02 | ||
| ZA82/8866 | 1982-12-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1214943A true CA1214943A (en) | 1986-12-09 |
Family
ID=25576409
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000442399A Expired CA1214943A (en) | 1982-12-02 | 1983-12-01 | Recovery of metal values from a pulp containing such values in dissolved form |
Country Status (9)
| Country | Link |
|---|---|
| AU (1) | AU557581B2 (en) |
| BR (1) | BR8306618A (en) |
| CA (1) | CA1214943A (en) |
| ES (1) | ES527716A0 (en) |
| FI (1) | FI74301C (en) |
| NZ (1) | NZ206461A (en) |
| PH (1) | PH19865A (en) |
| SE (1) | SE8306607L (en) |
| ZM (1) | ZM8483A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20120227545A1 (en) * | 2009-07-21 | 2012-09-13 | Anglo Operations Limited | Aqueous leaching process for recovery of precious metals with addition of di-thiooxamide ligand |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1987006271A1 (en) * | 1986-04-07 | 1987-10-22 | Adrian Pope | Leaching and adsorption of a precious metal |
-
1983
- 1983-11-23 ZM ZM84/83A patent/ZM8483A1/en unknown
- 1983-11-24 AU AU21645/83A patent/AU557581B2/en not_active Ceased
- 1983-11-30 SE SE8306607A patent/SE8306607L/en not_active Application Discontinuation
- 1983-12-01 CA CA000442399A patent/CA1214943A/en not_active Expired
- 1983-12-01 NZ NZ206461A patent/NZ206461A/en unknown
- 1983-12-01 FI FI834399A patent/FI74301C/en not_active IP Right Cessation
- 1983-12-01 BR BR8306618A patent/BR8306618A/en unknown
- 1983-12-01 ES ES527716A patent/ES527716A0/en active Granted
- 1983-12-02 PH PH29913A patent/PH19865A/en unknown
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20120227545A1 (en) * | 2009-07-21 | 2012-09-13 | Anglo Operations Limited | Aqueous leaching process for recovery of precious metals with addition of di-thiooxamide ligand |
| US8936667B2 (en) * | 2009-07-21 | 2015-01-20 | Anglo Operations Limited | Aqueous leaching process for recovery of precious metals with addition of di-thiooxamide ligand |
Also Published As
| Publication number | Publication date |
|---|---|
| NZ206461A (en) | 1985-09-13 |
| BR8306618A (en) | 1984-07-10 |
| FI74301C (en) | 1988-01-11 |
| AU557581B2 (en) | 1986-12-24 |
| FI834399A (en) | 1984-06-03 |
| ES8504954A1 (en) | 1985-04-16 |
| AU2164583A (en) | 1984-06-07 |
| FI834399A0 (en) | 1983-12-01 |
| ES527716A0 (en) | 1985-04-16 |
| ZM8483A1 (en) | 1984-06-21 |
| FI74301B (en) | 1987-09-30 |
| SE8306607D0 (en) | 1983-11-30 |
| SE8306607L (en) | 1984-06-06 |
| PH19865A (en) | 1986-08-13 |
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