CA2225370A1

CA2225370A1 - A process for recovering zinc values

Info

Publication number: CA2225370A1
Application number: CA002225370A
Authority: CA
Inventors: Walter Martin Macdonald; Ecaterina Gabriela Roseanu; Edward Bruce Holbein
Original assignee: SURINI INTERNATIONAL Ltd
Current assignee: SURINI INTERNATIONAL Ltd
Priority date: 1997-12-19
Filing date: 1997-12-19
Publication date: 1999-06-19
Also published as: AU1777199A; WO1999032675A1

Abstract

A method for obtaining complex zinc cyanide anions from a precipitate comprising zinc hydroxide and calcium sulfate. The method comprises subjecting such a precipitate to a zinc leaching step comprising contacting the precipitate with calcium cyanide in an aqueous liquid medium so as to obtain an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions and a remaining product precipitate comprising calcium sulfate.

Description

CA 0222~370 l997-l2-l9 TITLE: A PROCESS FOR RECOVERING ZINC VALUES

BACKGROUND OF THE lNV~NLlON

The present invention generally relates to processes which exploit ion exchange materials for recovering precious metal values (e.g. gold) from an (aqueous) cyanide solution. The present invention, in particular, relates to the treatment of an ion exchange material loaded with complex copper cyanide anions.
The present invention, more particularly, relates to the recovery o of zinc and cyanide values from an acidic solution containing hydrocyanic acid, the recovered zinc values and recovered cyanide values being used to strip copper from an ion exchange material wherein the copper is loaded as complex copper cyanide anions.

A metal bearing aqueous cyanide solution may, for example, be obtained from a process which involves leaching precious metal values from a metal-bearing material such as an ore, slime, concentrate, tailings and the like; in such a process the metal-bearing material is contacted with a suitable (aqueous) cyanide solution (e.g. an aqueous solution of sodium, potassium, calcium or other similar cyanides) to leach metal values therefrom and obtain a cyanide leach liquor comprising complex metal cyanides, e.g. of gold, silver, copper and the like. The leach liquor may then be contacted with a suitable ion exchange material so as to adsorb metal values and obtain an exchange material loaded with a mixture of precious metals and base metals.

CA 0222~370 l997-l2-l9 However, when a base metal such as copper is present in the material to be leached, copper values are also leached in the form of complex copper cyanide anions which can travel along with the precious metal values through the exchange material treatment circuits. Any copper complexes in recycled cyanide solution may also represent a fouling agent resulting in unwanted deposits being laid down in the leaching\metal recovery process circuits (see for example U.S. patent no. 2,124,421 the entire contents of which are incorporated herein by reference).

o Copper values may be recovered from an anion exchange resin by contacting the metal loaded material with a desorption agent.
The copper desorption agent may comprise complex zinc cyanide anions for the (selective) preliminary removal or separation of adsorbed copper values from an (strong or weak base) anion exchange material, (the anion exchange material may additionally be loaded with adsorbed cyanide complexes of precious metal values such as gold and silver). The copper desorption agent may for example be an alkaline solution (e.g. of pH 13 to 14) comprising sodium cations and complex zinc cyanide anions (e.g.
0.1 to 0.5 molar zinc cyanide anions). The zinc and cyanide values loaded on the anion exchange material may, in turn, be removed from the exchange material by subjecting the anion exchange material to an acid zinc stripping treatment step for removing zinc values therefrom. The acid zinc stripping treatment step may comprise contacting the zinc loaded anion exchange material with an acidic zinc eluting solution so as to obtain an acidic product eluate comprising zinc cations and CA 0222~370 l997-l2-l9 hydrocyanic acid and an acid treated anion exchange material (loaded with substantially all of the initial precious metal values), if initially present thereon). Sulphuric acid may advantageously be used for the zinc stripping process owing to its low cost and relative freedom from corrosion problems. The use of sulfuric acid, however, means that the resultant acidic solution comprises sulfate anions (So42~) in addition to the zinc cations and hydrocyanic acid.

Zinc values may be recovered from the acidic solution by use of o a cation exchange material. The recovery of zinc onto a cation exchange resin has its own problems with respect to efficiency and costs. A cation exchange resin may, for example, have a low capacity for zinc such that a large inventory of cation resin may be required, i.e. if recovering large amounts of copper. It is known to elute zinc values from a cation exchange resin using for example an aqueous NaCN solution. However, the elution of a large volume of cation resin having a relatively low zinc loading (i.e. a relatively low quantity of zinc per unit volume of resin) may thus result in a large volume of low strength complex zinc-cyanide anion solution, i.e. the eluant may have too low a concentration of the zinc complex for effective re-use in elution of copper-loaded resin without de-watering.

It is also known, for example, that cyanide values may be recovered from an acidic cyanide solution containing metal (e.g.

zinc) values by stripping hydrogen cyanide with air and passing the air through a suitable alkaline solution for absorbing the CA 0222~370 l997-l2-l9 hydrogen cyanide in such solution (see U.S. patent nos. 2,124,421 and 4,708,804); the remaining solution with any Metal (e.g.
copper or zinc) may be sent to a tailing pond or otherwise dealt with. In accordance with this approach it is known to use NaOH
for the recovery of cyanide values as NaCN which then may be used to form complex zinc-cyanide anions for recycling the cyanide values back to the copper stripping step mentioned above.

It should be pointed out that effective elution of copper-cyanide from an adsorbent may require a substantial amount of complex 0 zinc cyanide anions in the initial eluting solution, e.g. up to 1.7 moles of zinc cyanide complex for each copper to be eluted so as to ensure efficient elution. Advantageously, the cyanide utilized to elute the copper should be re-cycled. However, if NaOH is used to reform cyanide, after HCN volatilization of the eluant, the process would not be cost effective as 1 NaOH
equivalent is required for each HCN. NaOH is approximately 50%
of the cost of NaCN; thus this approach is not economically attractive.

On the other hand, the cost of Ca(OH) 2 iS relatively low as compared to the cost of NaOH. The ability to use Ca(OH) 2 would thus provide an economic benefit, i.e. if an economically attractive means for facilitating the recovery of utilizable Ca(CN) 2 for recycling would be available.

However, if sulfuric acid, for example, is used to strip zinc values from an anionic exchange material a major stumbling block CA 0222~370 l997-l2-l9 with respect to the use of Ca(CN) 2 for elution of adsorbed cyanide resides with respect to gypsum formation when (excess) Ca cations are present with (excess) so42~ anions.

Accordingly, the problem of how to deal with copper still persists in the precious metal (e.g. gold) processing arts, i.e.
with respect to the manner of how to adequately and economically deal with the presence of base metals such as copper in the leaching and metal recovery circuits. The metal processing industry is thus continuing to search for alternate process o techniques to meet this challenge.

It would be advantageous to be able to separate zinc and copper cyanide values so as to be able to remove copper from ion exchange circuits for recovering other types of metal values.

It would be advantageous to be able to recover zinc values from an acidic solution comprising zinc cations, sulfate anions and hydrocyanic acid without the use of a cation exchange resin.

It would be advantageous to be able to segregate zinc values, sulfate values and cyanide values present in an acidic solution comprising zinc cations, sulfate anions and hydrocyanic acid such that the zinc and cyanide values may be re-used and the sulfate values be removed from the process circuit for removing copper from a copper loaded anion exchange material. It, in particular, would be advantageous to be able to separate zinc values from gypsum.

CA 0222~370 1997-12-19 It would be advantageous to be able to effectively use substances such as complex zinc cyanide anions, H2SO4, CaO, Ca(OH) 2 Ca(CN) 21 etc.. for the recovery of zinc and cyanide values as part of various steps which may be used in a process for stripping copper values form an anion exchange material.

STATEMENT OF lNv~NllON

In accordance with the present invention it has been discovered that so42~ anions and Ca can be removed during the internal recycling of the reagents used for elution of copper from an anion exchange material by promoting gypsum (i.e. calcium sulfate) formation and recovering the gypsum as a product. Thus the present invention permits the utilization of complex zinc cyanide anions, H2SO4, CaO, Ca(O~) and Ca(~N) in various processes related to the removal of copper values from anion exchange resins. In accordance with the present invention it is possible, for example, to recycle zinc by precipitation and then re-solubilizing the zinc as complex zinc-cyanide anions using Ca(CN) 2-In particular, the present invention relates to the followingaspects, namely:
a. The separation of zinc from copper by precipitation owing to differential solubilities;
b. The reconversion of the zinc to complex zinc-cyanide anions using Ca(CN) 2; and c. The removal of unwanted so42~ and Ca from the final recovered CA 0222~370 l997-l2-l9 zinc cyanide values in the form of gypsum (i.e. calcium sulfate) which can be separated from the product zinc cyanide values owing to the differential solubilities of complex zinc cyanide anions and gypsum.

In particular, the present invention provides a method for obtaining complex zinc cyanide anions from a composition (e.g.
a precipitate) comprising zinc hydroxide and calcium sulfate;
i.e. zinc values are separated from calcium sulphate. The zinc separation may be effected by a method comprising subjecting a o precipitate to a zinc leaching step comprising contacting the precipitate with calcium cyanide in an aqueous liquid medium so as to obtain an aqueous alkaline zinc containing product solution comprising complex zinc cyanide anions and a remaining product precipitate comprising calcium sulfate.

With respect to the zinc leaching step the initial calcium cyanide concentration may be for example 10,000 ppm or higher (e.g. 77,000 to 125,000 ppm). The product solution of the leaching step may, for example, have a zinc content of 5000 ppm or higher (e.g. a zinc content of 18,700 ppm) and a pH above 10, such as a pH of from 10 to 13 (e.g. a pH of from 10 to 12.5).
In any event, the process conditions for the zinc leaching step are of course chosen so as to facilitate or promote the solubilization of zinc values in the precipitate (comprising zinc hydroxide and calcium sulfate) into an aqueous medium. For example, enough or sufficient calcium cyanide is used so as to promote the desired or predetermined degree of Zn solubilization, CA 0222~370 l997-l2-l9 i.e. so as to obtain a remaining particulate product have a depleted zinc concentration as compared to the initial level of zinc in the initial zinc containing composition or precipitate.

The present invention also provides a method for obtaining complex zinc cyanide anions, comprising i) adjusting the pH of an aqueous acidic solution (e.g.
having a pH of from about 0.1 to 3.5, in particular a pH of from 1.0 to 1.5) comprising zinc cations and sulfate anions by admixing, with the aqueous acidic solution, a caustic o material capable of promoting the formation of calcium sulfate and zinc hydroxide therewith so as to obtain a product liquor and a precipitate comprising zinc hydroxide and calcium sulfate, and ii) subjecting said precipitate to a zinc leaching step comprising contacting said precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing product solution comprising complex zinc cyanide anions.
The caustic material capable of promoting the formation of calcium sulfate and zinc hydroxide may, for example, comprise calcium oxide (or lime), calcium hydroxide, or a chemically equivalent material. The process conditions for the adjustment of the pH Of an aqueous acidic solution are of course chosen so as to facilitate or promote the precipitation of a precipitate comprising zinc hydroxide and calcium sulfate. The product CA 0222~370 l997-l2-l9 liquor may have, for example, a pH of between from about 6 to about 11 (e.g. a pH of from 8.5 to 9).

The above processes for obtaining complex zinc cyanide anions may for example be carried out under ambient temperature and pressure conditions (e.g. at a temperature of from 5~ C to 40~ C).

In accordance with the present invention a method for obtaining complex zinc cyanide anions may include a precipitate recovery step for separating the precipitate from said product liquor of o step i) before subjecting said precipitate to said zinc leaching step ii).

In another aspect the present invention provides a method for removing copper values from an anion exchange material. In accordance with this aspect of the present invention the aqueous acidic solution to be subjected to the pH adjustment may be derived from a HCN gas stripping stage or step; the aqueous acidic solution fed to the gas stripping stage may be obtained by pH adjustment of an eluate obtained from the stripping of copper from an anion exchange material; the pH adjusted eluate obtained from the stripping of copper from an anion exchange material may as desired be passed through a zinc stripping stage for stripping Zn from an anion exchange resin before being passed on to a CN gas stripping stage.

The present invention thus further provides a method for removing copper values from an anion exchange material, said anion CA 0222~370 l997-l2-l9 exchange material being loaded with initial copper values, said method comprising i) subjecting an anion exchange material loaded with adsorbed complex copper cyanide anions, to a copper stripping treatment step for removing copper values therefrom comprising contacting said anion exchange material with an aqueous alkaline copper eluting solution comprising complex zinc cyanide anions so as to obtain an aqueous alkaline eluate comprising complex copper cyanide anions and complex zinc cyanide anions and a zinc loaded o anion exchange material loaded with adsorbed complex zinc cyanide anions, ii) adjusting the pH of said aqueous alkaline eluate obtained from step i) by admixing sulfuric acid therewith so as to obtain an aqueous acidic solution having a pH of from 0.1 to 3.5 and a copper containing precipitate, said aqueous acidic solution comprising zinc cations, sulfate anions, and hydrocyanic acid, said copper containing precipitate comprising copper values, iii) gas stripping HCN from said aqueous acidic solution obtained from step ii) so as to obtain a HCN laden gas and a stripped aqueous acidic solution comprising zinc cations and sulfate anions, iv) adjusting the pH of said stripped aqueous acidic solution obtained from step iii) by admixing, with the aqueous acidic solution, a caustic material capable of forming calcium sulfate and an insoluble heavy metal hydroxide therewith so as to obtain a product liquor and a CA 0222~370 l997-l2-l9 product precipitate comprising zinc hydroxide and calcium sulfate, v) subjecting said product precipitate obtained from step iv) to a zinc leaching step comprising contacting said product precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions, and vi) recycling complex zinc cyanide anions as obtained from o step v) to said copper stripping treatment step of step i) for removing copper values from said anion exchange material loaded with complex copper cyanide anions.

The present invention also provides a method for removing copper values from an anion exchange material, said anion exchange materlal being loaded with initial copper values, said method comprlslng i) subjecting an anion exchange material loaded with adsorbed complex copper cyanide anions, to a copper stripping treatment step for removing copper values therefrom comprising contacting said anion exchange material with an aqueous alkaline copper eluting solution comprising complex zinc cyanide anions so as to obtain an aqueous alkaline eluate comprising complex copper cyanide anions and a zinc loaded anion exchange material loaded with adsorbed complex zinc cyanide anions, ii) subjecting said zinc loaded anion exchange material to CA 0222~370 l997-l2-l9 an acidic zinc stripping treatment step for removing zinc values therefrom comprising contacting said zinc loaded anion exchange material with an aqueous acidic zinc eluting solution comprising sulfuric acid so as to obtain an acidic zinc containing eluate and a treated anion exchange material, said acidic zinc containing eluate comprising zinc cations and hydrocyanic acid, iii) adjusting the pH of said aqueous alkaline eluate obtained from step i) by admixing sulfuric acid therewith so as to obtain an aqueous acidic solution having a pH of o between about 0.1 and about 3.5 and a copper containing precipitate, said aqueous acidic solution comprising zinc cations, sulfate anions, and hydrocyanic acid, said copper containing precipitate comprising copper values, at least a portion of said acidic zinc containing eluate obtained from step ii) being used in step iii) for adjusting the pH
of the alkaline eluate, iv) gas stripping HCN from said aqueous acidic solution so as to obtain a HCN laden gas and a stripped aqueous acidic solution comprising zinc cations and sulfate anions, V) adjusting the pH of said stripped aqueous acidic solution obtained from step iv) by admixing, with the stripped aqueous acidic solution, a caustic material capable of forming calcium sulphate and an insoluble heavy metal hydroxide therewith, so as to obtain a product liquor and a product precipitate comprising zinc hydroxide and calcium sulfate, vi) subjecting said product precipitate obtained from step CA 0222~370 1997-12-19 v) to a zinc leaching step comprising contacting said product precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions, and vii) recycling complex zinc cyanide anions as obtained from step vi) to said copper stripping treatment step of step i) for removing copper values from said anion exchange material loaded with complex copper cyanide anions.

The present invention additionally provides a method for removing copper values from an anion exchange material, said anion exchange material being loaded with initial copper values, said method comprising i) subjecting an anion exchange material loaded with adsorbed complex copper cyanide anions, to a copper stripping treatment step for removing copper values therefrom comprising contacting said anion exchange material with an aqueous alkaline copper eluting solution comprising complex zinc cyanide anions so as to obtain an aqueous alkaline eluate comprising complex copper cyanide anions and complex zinc cyanide anions and a treated zinc loaded anion exchange material loaded with adsorbed complex zinc cyanide anions, ii) adjusting the pH of said aqueous alkaline eluate obtained from step i) by admixing sulfuric acid therewith so as to obtain an aqueous acidic solution having a pH of CA 0222~370 l997-l2-l9 between about 0.1 and about 3.5 and a copper containing precipitate, said aqueous acidic solution comprising zinc cations, sulfate anions, and hydrocyanic acid, said copper containing precipitate comprising copper values, iii) subjecting said zinc loaded anion exchange material to an acidic zinc stripping treatment step for removing zinc values therefrom comprising contacting said zinc loaded anion exchange material with an aqueous acidic zinc eluting solution comprising sulfuric acid so as to obtain an acidic zinc containing eluate and a treated anion exchange o material, said acidic zinc containing eluate comprising zinc cations, sulfate anions and hydrocyanic acid, at least a portion of said aqueous acidic solution obtained from step ii) being used in step iii) for removing zinc values from said zinc loaded anion exchange material, iV) gas stripping HCN from at least a portion of said acidic zinc containing eluate obtained from step iii) so as to obtain a HCN laden gas and a stripped aqueous acidic solution comprising zinc cations and sulfate anions , v) adjusting the pH of said stripped aqueous acidic solution obtained from step iv) by admixing, with the stripped aqueous acidic solution, a caustic material capable of forming calcium sulphate and an insoluble heavy metal hydroxide therewith, so as to obtain a product liquor and a product precipitate comprising zinc hydroxide and calcium sulfate, vi) subjecting said product precipitate obtained from step v) to a zinc leaching step comprising contacting said CA 0222~370 l997-l2-l9 product precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions, and vii) recycling complex zinc cyanide anions as obtained from step vi) to said copper stripping treatment step of step i) for removing copper values from said anion exchange material loaded with complex copper cyanide anions.

o The anion exchange material loaded with initial copper may also as desired or as necessary also be loaded with (i.e. comprise) other metal values such as, for example, precious metal values, such as for example, gold, silver, etc..

In accordance with the present invention a precipitate recovery step may be provided for separating aqueous acidic solution from the copper containing precipitate before the aqueous acidic solution is subjected to said gas stripping.

Similarly in accordance with the present invention a precipitate recovery step may be provided for separating the (product) precipitate comprising calcium sulfate and product liquor before subjecting said product precipitate to the zinc leaching step In accordance with the present invention the HCN laden gas obtained from the gas stripping step may be contacted with a caustic substance comprising Ca so as to form calcium cyanide and CA 0222~370 l997-l2-l9 so obtained calcium cyanide is used in the zinc leaching step for obtaining said aqueous alkaline zinc containing solution.

In accordance with the present invention the anion exchange material may as mentioned above comprise both complex copper and complex zinc cyanide anions. As desired or as necessary the anion exchange material may comprise essentially no complex cyanide anions, e.g. by appropriately adjusting the amount of zinc complex in the copper eluting solution.

o The aqueous acidic zinc eluting solution may for example be a solution of 6% v/v sulfuric acid.

In drawings which illustrate example embodiments of the invention:

Figure 1 is a block diagram showing an example flow sheet of an adsorption circuit for the adsorption of copper values onto anion exchange material;
Figure 2 is a block diagram showing an example flow sheet of a metal stripping circuit for stripping copper from a copper loaded anionic exchange material Figure 3 is a block diagram showing a modified version of the example flow sheet shown in figure 2; and Figure 4 is a block diagram showing more detail with respect to various stages of the flow sheet of figure 1.

Referring to figure 1, this figure illustrates a flow sheet for CA 0222~370 l997-l2-l9 a batch type adsorption circuit for contacting a copper bearing cyanide solution with anion exchange material; this type of circuit is known. The adsorption circuit comprises seven (7) contactor stages designated by the reference numerals 1, 2, 3, 4, 5, 6, and 7. Each of these contactors comprises a suitable vessel within which may be contained particles of a suitable anion exchange material as well as cyanide solution. The contactors are connected by a suitable piping/pumping system whereby cyanide solution may be delivered to and removed from each of the contactors in series fashion; the cyanide solution o passes through the series of contactors in the direction of the arrows designated by the reference numerals 8 to 15. Suitable screening means (not shown) is also provided for each of the contactors for inhibiting the transfer of particles of anion exchange material between contactors as the cyanide solution flows from one contactor stage to the next in line.

The cyanide solution entering the first contactor stage 1 in the direction of arrow 8 may be an aqueous solution containing complex copper-cyanide anions; this solution may also include other metal complex cyanide anions such as for example anions of gold, silver, etc..

The anionic exchange material may be any adsorbent material capable of adsorbing complex copper cyanide anions as well as if desired other complex metal cyanide anions so as to remove such anions from the aqueous solution (the adsorbent may for example be VitrokeleTM V-912 adsorbent from Panfida Pty Ltd. of Perth CA 0222~370 1997-12-19 Australia). A suitable adsorbent material may be used in an amount so as to at least significantly if not substantially free the initial solution of its initial content of soluble copper-cyanide and other cyanide-containing species; the amount of adsorbent is predetermined in known fashion; e.g. if the adsorbent has an available capacity of 10 g of complex copper cyanide anions per 100 g resin, a cyanide solution containing 5 g complex copper cyanide anions may be contacted with 50 g of resin.

o The circuit described above requires that the adsorbent be maintained in each of the contactors. As an alternative the adsorbent may be displaced in countercurrent fashion by any suitable known means such that as the solution passes through the contactors in the direction of the arrows 8 to 15, the adsorbent passes through the contactors in the opposite direction, namely;
in the direction of the dotted arrows 8a to 15a. For this type of circuit it is possible to have a continuous process of separation of the adsorbent from the solution at the first contactor or stage 1, i.e. in the direction of the arrow 15a.
In this case the contactors may also be connected by another suitable piping/pumping system whereby adsorbent may be delivered to and removed from each of the contactors in series fashion countercurrent to the direction of flow of the cyanide solution.

Referring to figure 2, this figure illustrates an example flow sheet for a copper stripping circuit for stripping copper from CA 0222~370 l997-l2-l9 a copper bearing anionic exchange material using an aqueous alkaline solution comprising complex zinc cyanide anions and recovering and recycling zinc and cyanide values for such copper strlpplng .

Anionic exchange material loaded with copper and possibly other metal cyanide-containing complexes obtained for example from a circuit such as illustrated in figure 1 (i.e. from arrow 15a) may be fed to a Cu stripping stage 20 via feed line 21. An aqueous alkaline elution solution is also fed to the stage 20 via feed o line 22 for eluting copper (and possibly other metal values from the adsorbent material). The aqueous alkaline elution solution may have a pH of from 10 to 12.5 and comprises complex zinc cyanide anions. The complex zinc cyanide anions may be present at levels for example of from about 0.1 to about 0.5 molar (e.g.
at levels of 0.24 molar or lower).

The alkaline eluate leaving the Cu stripping stage 20 comprising complex copper cyanide anions, any excess complex zinc cyanide anions and possibly other complex metal cyanide anions is sent via line 23 to an acidification/precipitation stage 24. The alkaline treated adsorbent material loaded with complex zinc cyanide anions is sent from the Cu stripping stage 20 via line 25 to a zinc stripping stage 26.

The alkaline treated adsorbent is contacted in the zinc stripping stage 26 with an aqueous acidic solution comprising sulphuric acid so as to obtain an acid-eluted adsorbent and an acidic CA 0222~370 1997-12-19 eluant liquor containing sulphuric acid, zinc cations and HCN.
The aqueous acidic solution is fed into the stage 26 via line 27.
The acid-eluted adsorbent leaving the zinc stripping stage 26 has a reduced zinc loading and may even, as desired, be substantially free of zinc cyanide species. At least a portion of the acidic eluant liquor is passed via line 28 to the acidification/precipitation stage 24; any acidic acid liquor not passed to stage 24 may be passed (not shown) to the gas stripping stage described below (please see figure 3). The acid-eluted adsorbent, if desired, is recycled via line 29, to a copper o adsorption circuit such as described for example with respect to figure 1, i.e. to arrow 8a; before being sent to stage 7 the absorbent may as desired or as necessary be rinsed with water and ph adjusted.

In the acidification/precipitation stage 24, the copper containing alkaline eluate is admixed with the acidic zinc containing eluant liquor so as to obtain a pH adjusted liquor or solution of the required or desired low pH; if desired or necessary, additional sulfuric acid may be fed via feed line 30 to the acidification/precipitation stage 24 to obtain a pH
adjusted liquor of desired or required pH. The pH of the pH
adjusted liquor is in any event adjusted so as to on the one hand result in the desired or required proportion of the contained copper being precipitated (e.g. as CuCN and/or as another insoluble precipitate of copper, such as CuSCN) and on the other hand promote the retention of zinc in solution as soluble zinc cations as well as cyanide values in the form of HCN; the pH may CA 0222~370 1997-12-19 for example be 1.0 to 1.5 and the temperature and pressure conditions may be ambient conditions.

The insoluble copper precipitate may be separated and recovered from the pH adjusted liquor or solution by any suitable physical means, such as for example filtration, thickening etc. so as to obtain a copper containing precipitate product and a copper-depleted acidic liquor containing soluble zinc ions and HCN. The separated copper containing precipitate is removed via line 31 for disposal in any suitable fashion (i.e. be sent on to a copper o smelter, refinery etc.). The copper-depleted acidic liquor containing soluble zinc ions and HCN is fed via line 32 to a gas stripping stage 33.

In the gas stripping stage 33 cyanide values are separated from the acidic liquor in known fashion by volatilization into a gas stream introduced into the stripping stage 33. Thus a gas stream, such as for example, air, is introduced into the stripping stage 33 via line 34 so as to obtain a gas stream rich in cyanide values and a cyanide depleted acidic liquor which, if desired or required, may be substantially free of HCN while still containing soluble zinc cations. The cyanide rich gas is fed via line 35 to a CN recovery stage 37 whereas the cyanide depleted acidic liquor is fed via line 38 to a calcium sulfate precipitation stage 40.

Although the removal of HCN by gas stripping has been described above as occurring after the separation and recovery of the CA 0222~370 1997-12-19 copper precipitate, such HCN separation may possibly be carried out before the copper precipitate is separated; however this is less attractive due to the presence of the precipitate which means that extra care may have to be taken to avoid clogging, the conversion of Cu values to copper sulfate, etc..

The recovery of the HCN from the cyanide rich gas stream may be carried out in accordance with the present invention by contacting the cyanide rich gas stream with an alkaline solution comprising dissolved or suspended Ca(OH) 2 SO as to obtain an alkaline cyanide containing solution comprising Ca(CN) 2/ i. e. in analogous fashion as when sodium hydroxide is used for this purpose. The alkaline solution is fed to the CN recovery stage 37 via line 41 whereas cyanide depleted gas (i.e. gas at least essentially cyanide free) exits stage 37 via line 43 for venting to the atmosphere. The alkaline cyanide containing solution exits the CN recovery stage 37 via line 44.

The pH of the HCN depleted acidic liquor from stage 33 may be adjusted in the gypsum precipitation stage 33 to a pH sufficient to precipitate at least a substantial portion of the zinc as zinc hydroxide species (e.g. a pH of 8.5 to 9.0) by neutralization of the acidic liquor with a calcium substance able to provide (CaS04) and zinc hydroxide (Zn(OH) 2)SO as to obtain a precipitate product comprising zinc hydroxide and calcium sulfate and a liquor (e.g. of pH 8.5 to 9.0). The calcium substance such as for example lime or calcium hydroxide is fed to the calcium sulfate precipitation stage via line 49. The zinc/gypsum CA 0222~370 1997-12-19 precipitate is separated from the neutralised liquor by any suitable physical means, such as for example filtration. The separated liquor may be sent via line 50 for disposal or for additional pH treatment, e.g. it may be sent on to a hold pond.
The recovered zinc/gypsum precipitate is fed via line 55 to a zinc/cyanide recovery stage 58 for recovering zinc values from the zinc/gypsum precipitate as complex zinc cyanide anions.

In the zinc/cyanide recovery stage 58, the zinc/gypsum precipitate is contacted in an aqueous medium (e.g. water) with Ca (CN) 2 SO as to leach zinc values from the precipitate as complex zinc cyanide anions, i.e. so as to form an aqueous alkaline solution which may for example have a pH of from 10 to 12.5 and which comprises complex zinc cyanide anions. The Ca (CN) 2 may be added in a predetermined amount which promotes the solubilization of zinc values and reduces the zinc values in the precipitate to a desired level; these amount may be predetermined in known fashion. The contact time may for example range from 30 to 60 minutes. All or a portion of the required Ca (CN) 2 may be provided in the form of the recovered Ca (CN) 2 obtained from the above mentioned CN recovery stage 37 via line 44, i.e. by exploiting the alkaline cyanide containing aqueous fluid exiting the CN recovery stage 37. Any additional Ca (CN) 2 may be provided by another source via line 60. Alternatively, as desired, all of the required Ca (CN) 2 may be derived from line 60.

Once the zinc values in the precipitate have been reduced to the desired or required levels the remaining treated precipitate CA 0222~370 1997-12-19 comprising insoluble CaSO4 (i.e. gypsum) may be separated from the product aqueous alkaline comprising complex zinc cyanide anions by any known suitable physical means, such as for example by filtration; if desired the calcium sulfate may be rinsed with water to remove residual zinc complex anions. The separated gypsum is removed in figure 2 via line 61; the calcium may be sent to a gypsum recycler for use in construction, etc..

The complex zinc cyanide anions separated from gypsum in the stage 58 may be recycled via line 22 to the copper stripping o stage 20 for further use in eluting copper-cyanide and other cyanide-containing species from a metal loaded anion exchange material.

In accordance with the present invention, if the eluant leaving the stripping stage via line 23 and sent to the acidification/precipitation stage 24 comprises SCN as an additional cyanide-containing species, the SCN may precipitate in stage 24 with a portion of the copper as CuSCN; all things being equal, the SCN substitutes for a CN in the precipitation of the copper so as to form CuSCN and not CuCN and leave more CN
in the acidic solution than if no SCN were present.

Referring to figure 3 this figure illustrates a modified version of the flow sheet shown in figure 2. The same reference numerals are used to designate the same elements. As may be seen from figure 3 the acidic eluant liquor leaving the Zn separation stage is directed via line 28a directly to the gas stripping stage 33 CA 0222~370 l997-l2-l9 rather than being sent to the acidification stage 24. In this case the acidification for stage 24 is accomplished by relying on the acid feed line 30.

As a further modification the flow sheet includes a dotted line 32a along which, as desired, a portion or all of the acidic liquor leaving the acidification stage 24 may be sent to the Zn stripping stage 26; if all of the liquor is sent to the Zn stripping stage 26 it is of course understood that no flow will occur along line 32.

Figure 4 shows by way of example, in more detail the flow sheet shown in figure 1. As may be seen the acidification stage 24 comprises a contact tank 80, a thickener 81 and a filter 82. The CN recovery stage 37 comprises three contact columns 85, 86, and 87 arranged in series so that air passes in countercurrent fashion therethrough with respect to the calcium substance for reaction with cyanide. The Zn precipitation stage 40 also comprises a contact tank 90, a thickener 91 and a filter 92. The Zn solubilization stage 58 comprises a contact tank 95 and a filter 96.

EXAMPLES

The following non-limiting examples are provided by way of example only to describe the invention.

CA 0222~370 l997-l2-l9 ~xample 1: Ad~orption of copper cyanide and other cyanide-cont~;n;ng species from an aqueous solution An aqueous solution containing copper-cyanide in the form of a slurry discharge waste stream obtained from an operating gold mill was contacted with VitrokeleTMV-912 adsorbent (as obtained from Panfida Pty Ltd. of Perth Australia). The slurry waste was routed through a series of contactors containing the VitrokeleTM
adsorbent so as to permit adsorption of the copper-cyanide and other cyanide-containing species; contact was carried out in o accordance with a adsorption circuit shown in figure 1. The slurry waste was continually passed through the contactors which were set up in series so that the treated slurry waste leaving the first contactor entered the second, the waste leaving the second entered the third and so on, so that a total of seven contactings of the waste were achieved. Each contactor contained 7.5% by volume of the VitrokeleTM adsorbent which was retained in its respective contactor by using a screen of 0.6 mm opening size. This permitted the slurry waste containing particles of a size less than 0.6 mm to pass from contactor to contactor while the VitrokeleTM adsorbent of a size greater than 0.6 mm was retained in its respective contactor. The VitrokeleTM progressed through the contactor stages countercurrently in a continuous fashion, entering stage 7 (e.g. as regenerated VitrokeleTM) and progressed from contactor to contactor, i.e. from contactor stage 7 to contactor stage 6 and so on, until emerging from contactor stage 1 as metal loaded vitrokele. The VitrokeleTM residence time in each contactor stage was such that adequate time was CA 0222~370 l997-l2-l9 provided for adsorption of target metal species to occur (e.g.
a residence time of about 1 hour per stage). The transfer of vitrokele between stages was done by screening or pumps and was at a rate such that the solution leaving the (last ) contactor stage 7 was essentially free of the target metal species (e.g.
Cu removal greater than 99%, cyanide removal greater than 99%).
The VitrokeleTM transfer rate between stages being 1.66% of the VitrokeleTM inventory per minute. After sufficient slurry waste was passed through the contactor series, samples of the slurry waste were removed from each contactor and these were screened o using a 0.6 mm screen. The contents of copper and cyanide were measured in these samples and compared to samples of the starting slurry waste prior to contacting with VitrokeleTM adsorbent.

Results as shown in Table 1 were obtained.

A sample of the VitrokeleTM adsorbent exiting from contactor stage 1 (i.e. see figure 1) after passage of the slurry waste through the contactor series was analyzed. This VitrokeleTM
adsorbent was found to contain 70,000 ppm copper and 110,000 ppm cyanide. The results in the Table show that the VitrokeleTM
adsorbent removed copper and cyanide from the aqueous portion of the slurry waste, concentrating these onto the adsorbent VitrokeleTM and that the VitrokeleTM could be removed from the slurry waste with its load of copper and cyanide.

CA 02225370 l997-l2-l9 Table 1 Sampl- Total Cu in ~ of St-rting Total Titratabl- ~ of Starting Analyzed SolutionCu r-moved by Cyanide in Cyanid- ~ moved (ppm~ Vitrokele~Solution by Vitrokele~
(ppm) Slurry 970 0362 0 waste before contacting Slurry waste after contacting in Stage l712 27218 40 Stage 24B2 51139 62 Stage 3251 7466 82 Stage 462 9426 93 Stage 512 98 8 7 4 98 Stag- 6 2 4 99 7 4 9 98 6 Stage 71 5 99 9 2 8 99 2 CA 0222~370 l997-l2-l9 Example 2: Elution of copper-cyanide and other cyanide-containing ~pecies from adsorbent material.

A sample of copper-cyanide and other cyanide-containing species loaded adsorbent as prepared in Example 1 (i.e. exiting from stage 1 in figure 1) was contacted with a 0.24 molar solution of Zn(CN)4~2 in water. The loaded adsorbent was placed in a column and eluted using the Zn(CN) 4-2 solution which was passed upward through the column by pumping. The eluted adsorbent was removed from the bottom of the column and rinsed with water. The eluate solution o was collected as it exited the top of the column.

The loaded adsorbent prior to elution was found to contain 70,000 mg/Kg Cu and 2,400 mg/Kg Zn. Elution with a 0.24 molar Zn(CN) 4-2 solution including a 20~ excess of cyanide effectively eluted the adsorbed Cu; this corresponded to an addition of 1.0 moles Zn and 5.0 moles of CN per mole of Cu. The eluted adsorbent was found to contain only 20,000 mg/Kg of the initial 70,000 mg/kg Cu and 46,000 mg/kg Zn, i.e. adsorbed from the eluant in place of the Cu. The zinc elution liquor was found to contain the desorbed Cu-cyanide and surplus Zn-cyanide species.

Example 3: Efficiency of elution of copper-cyanide from adsorbent with Zn(CN) 42- solution.

Samples of loaded adsorbent as prepared in example 1 were eluted as described in example 2 using separate elution tests at various CA 0222~370 l997-l2-l9 strengths of Zn(CN) 42- solution so as to compare the efficiency of Cu elution as a function of the amount of Zn(CN) 42- used. The results in the Table 2 below show the percentage of the initially adsorbed Cu which was eluted at different total ratios of applied Zn to adsorbed Cu. In each test the volume of adsorbent was the same with only the strength of the eluant being varied; the temperature of the system was 20~ C.

Table 2 o Molar Ratio of Zn:Cu % of initially adsorbed Cu from Zn(CN) 42- used to elute eluted 0.67 49.5 1.00 70.2 1.34 84.4 1.67 90.4 As may be seen a substantial (90%) elution of Cu was achieved by applying approximately 1.67 moles of Zn (as Zn(CN) 42 ) to each mole of Cu initially adsorbed to the adsorbent.

Example 4: Elution of zinc and cyanide from zinc-cyanide eluted adsorbent which contains zinc cyanide complex anions and copper cyanide complex anions A sample of zinc-cyanide eluted adsorbent as obtained in example 2 CA 0222~370 l997-l2-l9 was placed in a column and eluted as described in example 2 except that 6% v/v H2S04 was used as the eluant and not zinc-cyanide solution.

The acid eluted adsorbent was found to contain 2,000 mg/kg zinc representing an elution efficiency of 96% of the initial zinc which had been adsorbed to the adsorbent. Copper values were retained on the acid eluted adsorbent as a precipitate, substantially in the form of CuCN.

o The acid eluent liquor was found to contain the eluted zinc which was desorbed from the adsorbent.

Example 5: Re-use of eluted adsorbent Acid eluted adsorbent as prepared in example 4 was rinsed with water, pH adjusted (e.g. to a pH above 10) and used for further adsorption tests for adsorption of copper-cyanide and other cyanide-containing species as described in example 1. Results similar to those shown in example 1 were obtained indicating the eluted adsorbent was fully usable for repeated cycles of usage, i.e. adsorption and elution.

Example 6: Influence of pH on solubility of Cu and Zn in combined eluate liquor of zinc and acid eluates Samples of zinc eluate liquor as obtained in example 2 were mixed CA 0222~370 1997-12-19 with samples of acid eluate liquor as obtained in example 4. A
mixture of 1 part of each was found to have a resulting pH of approximately 3.5. Various sub-samples of 1:1 mixture of combined eluate liquor were adjusted to different pH values using additions of H2SO4 or NaOH and amounts of Cu and Zn remaining in the solution phase after filtration to remove precipitated solids were measured.
Soluble zinc and copper as a function of pH were expressed as a percentage of the total copper and zinc in the combined eluate prior to filtration to remove solids. Results were as obtained are shown in table 3 below.

Table 3 Influence of pH of combined eluate liquor on solubility of contained copper and zinc pH % Zn % Cu soluble soluble 3.53 23.4 18.4 3.33 30.0 5.1

2.25 70.0 5.0 1.68 72.0 4.6 1. 42 73.0 1.2 1.29 83.0 1.4 1.17 89.0 1.7 1.07 89.5 1.9 1.03 94.7 2.6 1.00 97.0 2.1 CA 0222~370 l997-l2-l9 These results show that at a pH of approximately 3.5 or less a siginificant portion of the Cu is insoluble and is removed as a precipitate by filtration, while in this pH range, a significant portion of the zinc is soluble and remains in the filtrate after removal of the precipitated copper.

Example 7: Preparation of a combined zinc eluate/acid eluate liquor Equal portions of zinc-eluate liquor as prepared in example 2 were mixed with equal portions of acid eluate liquor as prepared in example 4 to obtain a combined eluate liquor. The pH of the combined liquor was found to be about 3.5. At this pH a grey-white precipitate was present in the liquor. The pH of the combined eluate liquor was lowered to about pH 1.0 by addition of H2SO4. At this pH the precipitate in the liquor was a light pink in colour.
The combined liquor was filtered to remove precipitated solids and to obtain a clear filtrate. The clear filtrate was found to contain 97% of the total zinc and this was present in the solution at approximately 3,800 mg/L. The clear filtrate solution was found to contain only 42 mg/L Cu which represented only 2.1% of the total copper. The remaining copper, 97.9% of the total copper, was found in the filtered solids which were maroon in colour.

Example 8: Separation of copper precipitate from combined CA 0222~370 l997-l2-l9 eluate A combined eluate was prepared as in example 7 and after mixing for ten minutes at pH 1.0 the liquor was allowed to stand. The contained precipitate was pink in colour and this rapidly settled as a free settling flocculated mass. A clear solution was evident above the precipitate within a few minutes and this could be decanted from the precipitate enable the harvesting of the substantial portion of the clear liquor. This liquor decant was found to be rich in zinc and low in copper. The remaining solution was readily separated from the copper-containing precipitate by filtration. Washing of the precipitate with acidic water at pH 1.0 removed most of the residual zinc while leaving the substantial portion of the copper in the precipitate on the filter.

Example 9: Recovery of HCN from acidic co~bined eluant Samples of acidic combined eluate at pH 1.0 after removal of Cu precipitates as obtained in examples 7 or 8, were percolated downwards through an air-stripping column in which an air stream was passed upwards over the percolating solution and out of the column. The air stream leaving the stripping column was passed through a number of lime traps configured in series in which the air was bubbled through a slurry of Ca(OH) 2 suspension. The acidic eluate was found to contain approximately 6000 mg/L of CN prior to air stripping and approximately 10 mg/L after air stripping. The air stripped combined liquor retained its content of soluble zinc during the air stripping operation. The HCN which was stripped CA 0222~370 l997-l2-l9 into the air stream was found in the lime trap at a concentration of approximately 110,000 mg/L of the lime slurry; i.e. the exhaust air had less then 5 ppm HCN. Thus a significant portion of the cyanide in the acidic combined eluate could be removed from the eluate and reconverted to Ca(CN) 2 and related species in the lime slurry trap. This process did not alter the zinc content of the combined eluate which remained in solution in the air stripped zinc-containing, low copper, low cyanide combined eluate.

Example 10: Recovery of zinc from combined eluate by adsorption to a cation e~ch~nge resin A sample of air-stripped, zinc-containing combined eluate as prepared in example 9 was used for a series of tests using different cation exchange resins so as to test their efficiency and capacity for recovery of the zinc from the eluate solution. The eluate solution contained zinc at approximately 3700 mg/L and this was tested either at its native pH of 1.0 or after adjustment to pH
5.0 with NaOH. A sample of the resin to be tested, either in its H+ or Na+ form, was placed in a column and zinc-containing eluate was passed through the column of cation exchange at a flow rate ranging from 2.0 - 9.2 bed volumes/hr. The capacities of the cation exchange resins for recovering the zinc from the eluate solution were compared by determining capacity in zinc equivalents per litre of resin.

In a separate test zinc containing eluate after copper removal but CA 0222~370 l997-l2-l9 before air-stripping to remove HCN as prepared in example 7 was tested.

The results are shown in the table below.

pH of Zn- Free CN Resin type tested Form Resin Zn contA;nin~ present of capacity eluate (ppm) resin Zn equivalents/L
1 <10 Purolite C-150 H+ 0.50 <10 Purolite C-150 H+ 0.38 <10 Purolite C-150 Na+ 0.50 1 <10 Diphonix DPA-801 H+ 0.17 1 <10 Diphonix DPA-801 Na+ 0.33 <10 Diphonix DPA-801 Na+ 0.72 1 7454 Purolite C-150 H+ 0.60 1 6505 Purolite C-150 Na+ 0.50 In all the tests above, cation resin capacities of <0.72 Zn equivalents per litre of resin bed were obtained. Typical cation resins have a metal capacity (total exchange) >2.8 equivalents per litre (i.e. in other applications involving recovery of metal cations). The low capacities observed for zinc were likely due to the presence of other competing cations eg. Ca2+ which restricted the capacity for zinc recovery. The presence of cyanide or the pH
of the solution did not greatly affect capacity nor did the form of the resin used, i.e. Na+ versus H+ form. The resin Diphonix DPA-801 was obtained form Eichrom Industries Inc., Darien Il. U.S.A.; the CA 0222~370 l997-l2-l9 resin Purolite C-150 was obtained from Purolite Company, division of Biotech Corporation Phila. PA, U.S.A..

~xample 11: Precipitation of zinc and sulphate from combined eluate liquor A sample of combined eluate liquor after removal of copper precipitates and HCN as prepared in example 9 was treated with Ca(OH) 2 to achieve a pH of 8.5. This treatment caused immediate precipitation of a large volume of grey-white material which was readily separated from the liquor by settling and decantation or by filtration. Tests of the precipitate revealed it to be rich in zinc which was present as Zn(OH) 2 species and Ca which was present as CaSO4 species. The filtrates or decants were found to be low in zinc (0.5 mg/L versus the initial 3700 mg/L) and sulphate ion. The latter species (SO4) had formed gypsum upon addition of the Ca(OH) 2 while the OH from the Ca(OH) 2 precipitated the zinc as Zn(OH) 2.

Example 12: Recovery of Zn as Zn(CN) 42- from Zn(OH) 2/CaSO4 solids A sample of Zn(OH)2/CaSO4 precipitate as prepared in example 11 was treated with Ca(CN)2/Ca(OH) 2 solution as prepared in example 9.
After a 10 minute period of mixing the reaction mixture was filtered. The filtrate was straw yellow in colour and found to contain soluble Zn and CN species primarily in the form of Zn(CN) 42--The filtered solids were found to be composed of CaSO4 solids andwere low in zinc. The test showed that about 96% of the zinc could CA 0222~370 1997-12-19 be recovered from the solids leaving the gypsum (CaSO4) in an insoluble form. The Zn(CN) 42- solution formed was at approximately 0.3 molar, a concentration suitable for re-use in elution of adsorbents as described in examples 2 and 3, i.e. without removal of water.

Example 13:

A sample of the recovered Zn(CN) 42- solution as prepared in example o 12 was used in tests to determine its utility as a copper elution eluate using the test protocol described in example 2. Freshly prepared reagent Zn(CN) 42- was also used for comparison with results obtained as below.

Zn(CN) 42-ConcentrationAmount Used % Cu Solution bed volumes Eluted Synthetic .24 2.0 71.5 From example 12 .28 2.0 81.6 This test showed that recovered Zn(CN) 42- was fully usable for re-use in elution of copper cyanide and other cyanide-containing species from a loaded adsorbent.

~5 Example 14: Adsorption, recovery and re-use of SCN in recovery of Cu CA 0222~370 1997-12-19 A sample of waste as described in example 1 but containing 600 ppm SCN in addition to the complex copper cyanide anion content was treated with VitrokeleTM V-912 adsorbent as described in example 1.
In this test only approximately 50% of the available SCN was allowed to adsorb to the adsorbent which still adsorbed approximately 99.5% of the Cu in the waste. Elution with Zn (CN) 42-as described in example 2 removed the substantial portion of the SCN along with the Cu. The zinc eluate was found to contain o approximately 500 ppm SCN. Elution of the adsorbent with H2SO4 after zinc elution removed only traces of SCN.

The combined eluate of these eluates prepared as described in example 7 resulted in a copper precipitate containing 868 mg of SCN. This represented 93.8% of the SCN present in the combined eluate liquor. This SCN adsorbed was eluted with the Zn ~CN) 42- and this SCN precipitated with Cu forming CuSCN as opposed to CuCN
which would have formed had SCN not been present. Available SCN
thus spares an equivalent amount of CN for recovery as described in example 9.

Claims

We claim:

1. A method for obtaining complex zinc cyanide anions from a precipitate comprising zinc hydroxide and calcium sulfate, said method comprising subjecting said precipitate to a zinc leaching step comprising contacting said precipitate with calcium cyanide in an aqueous liquid medium so as to obtain an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions and a remaining product precipitate comprising calcium sulfate.

2. A method for obtaining complex zinc cyanide anions, comprising i) adjusting the pH of an aqueous acidic solution comprising zinc cations and sulfate anions by admixing, with the aqueous acidic solution, a caustic material capable of forming calcium sulfate and an insoluble heavy metal hydroxide therewith so as to obtain a product liquor and a precipitate comprising zinc hydroxide and calcium sulfate, and ii) subjecting said precipitate to a zinc leaching step comprising contacting said precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions.

3. A method as defined in claim 2 wherein the product liquor of step i) has a pH of between from about 6 and to about 11.

4. A method as defined in claim 2 wherein product liquor of step i) has a pH of from 8.5 to 9Ø

5. A method as defined in claim 2 wherein the aqueous alkaline zinc containing solution of step ii)has a pH of from 10 to 13Ø

6. A method as defined in claim 2 comprising a precipitate recovery step for separating said precipitate from said product liquor of step i) before subjecting said precipitate to said leaching step.

7. A method for removing copper values from an anion exchange material, said anion exchange material being loaded with initial copper values, said method comprising i) subjecting an anion exchange material loaded with adsorbed complex copper cyanide anions, to a copper stripping treatment step for removing copper values therefrom comprising contacting said anion exchange material with an aqueous alkaline copper eluting solution comprising complex zinc cyanide anions so as to obtain an aqueous alkaline eluate comprising complex copper cyanide anions and complex zinc cyanide anions and a zinc loaded anion exchange material loaded with adsorbed complex zinc cyanide anions, ii) adjusting the pH of said aqueous alkaline eluate obtained from step i) by admixing sulfuric acid therewith so as to obtain an aqueous acidic solution having a pH of from 0.1 to 3.5 and a copper containing precipitate, said aqueous acidic solution comprising zinc cations, sulfate anions, and hydrocyanic acid, said copper containing precipitate comprising copper values, iii) gas stripping HCN from said aqueous acidic solution obtained from step ii) so as to obtain a HCN laden gas and a stripped aqueous acidic solution comprising zinc cations and sulfate anions, iv) adjusting the pH of said stripped aqueous acidic solution obtained from step iii) by admixing, with the aqueous acidic solution, a caustic material capable of forming calcium sulfate and an insoluble heavy metal hydroxide therewith so as to obtain a product liquor and a product precipitate comprising zinc hydroxide and calcium sulfate, v) subjecting said product precipitate obtained from step iv) to a zinc leaching step comprising contacting said product precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions, and vi) recycling complex zinc cyanide anions as obtained from step v) to said copper stripping treatment step of step i) for removing copper values from said anion exchange material loaded with complex copper cyanide anions.

8. A method as defined in claim 7 wherein product liquor of step iv) has a pH of between from about 6 and to about 11.

9. A method as defined in claim 7 wherein product liquor of step iv) has a pH of from 8.5 to 9Ø

10. A method as defined in claim 7 wherein the aqueous alkaline zinc containing solution of step v) has a pH of from 10 to 13Ø

11. A method as defined in claim 7 including a) a precipitate recovery step for separating said aqueous acidic solution from said copper containing precipitate of step ii), before said aqueous acidic solution is subjected to said gas stripping in step iii) and b) a precipitate recovery step for separating said product precipitate from said product liquor of step iv) before subjecting said product precipitate to said zinc leaching step v).

12. A method as defined in claim 7 wherein the HCN laden gas obtained from step iii) is contacted with a caustic substance comprising Ca so as to form calcium cyanide and so obtained calcium cyanide is used in step v) for obtaining said aqueous alkaline zinc containing solution.

13. A method for removing copper values from an anion exchange material, said anion exchange material being loaded with initial copper values, said method comprising i) subjecting an anion exchange material loaded with adsorbed complex copper cyanide anions, to a copper stripping treatment step for removing copper values therefrom comprising contacting said anion exchange material with an aqueous alkaline copper eluting solution comprising complex zinc cyanide anions so as to obtain an aqueous alkaline eluate comprising complex copper cyanide anions and a zinc loaded anion exchange material loaded with adsorbed complex zinc cyanide anions, ii) subjecting said zinc loaded anion exchange material to an acidic zinc stripping treatment step for removing zinc values therefrom comprising contacting said zinc loaded anion exchange material with an aqueous acidic zinc eluting solution comprising sulfuric acid so as to obtain an acidic zinc containing eluate and a treated anion exchange material, said acidic zinc containing eluate comprising zinc cations and hydrocyanic acid, iii) adjusting the pH of said aqueous alkaline eluate obtained from step i) by admixing sulfuric acid therewith so as to obtain an aqueous acidic solution having a pH of between about 0.1 and about 3.5 and a copper containing precipitate, said aqueous acidic solution comprising zinc cations, sulfate anions, and hydrocyanic acid, said copper containing precipitate comprising copper values, at least a portion of said acidic zinc containing eluate obtained from step ii) being used in step iii) for adjusting the pH of the alkaline eluate, iv) gas stripping HCN from said aqueous acidic solution so as to obtain a HCN laden gas and a stripped aqueous acidic solution comprising zinc cations and sulfate anions, v) adjusting the pH of said stripped aqueous acidic solution obtained from step iv) by admixing, with the stripped aqueous acidic solution, a caustic material capable of forming calcium sulphate and an insoluble heavy metal hydroxide therewith, so as to obtain a product liquor and a product precipitate comprising zinc hydroxide and calcium sulfate, vi) subjecting said product precipitate obtained from step v) to a zinc leaching step comprising contacting said product precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions, and vii) recycling complex zinc cyanide anions as obtained from step vi) to said copper stripping treatment step of step i) for removing copper values from said anion exchange material loaded with complex copper cyanide anions.

14. A method as defined in claim 13 wherein product liquor of step v) has a pH of between from about 6 and to about 11.

15. A method as defined in claim 13 wherein product liquor of step v) has a pH of from 8.5 to 9Ø

16. A method as defined in claim 13 wherein the aqueous alkaline zinc containing solution of step vi) has a pH of from 10 to 13Ø

17. A method as defined in claim 13 including a) a precipitate recovery step for separating said aqueous acidic solution from said copper containing precipitate of step iii), before said aqueous acidic solution is subjected to said gas stripping in step iv) and b) a precipitate recovery step for separating said product precipitate from said product liquor of step v) before subjecting said product precipitate to said zinc leaching step vi).

18. A method as defined in claim 13 wherein the HCN laden gas obtained from step iv) is contacted with a caustic substance comprising Ca so as to form calcium cyanide and so obtained calcium cyanide is used in step vi) for obtaining said aqueous alkaline zinc containing solution.

19. A method for removing copper values from an anion exchange material, said anion exchange material being loaded with initial copper values, said method comprising i) subjecting an anion exchange material loaded with adsorbed complex copper cyanide anions, to a copper stripping treatment step for removing copper values therefrom comprising contacting said anion exchange material with an aqueous alkaline copper eluting solution comprising complex zinc cyanide anions so as to obtain an aqueous alkaline eluate comprising complex copper cyanide anions and complex zinc cyanide anions and a treated zinc loaded anion exchange material loaded with adsorbed complex zinc cyanide anions, ii) adjusting the pH of said aqueous alkaline eluate obtained from step i) by admixing sulfuric acid therewith so as to obtain an aqueous acidic solution having a pH of between about 0.1 and about 3.5 and a copper containing precipitate, said aqueous acidic solution comprising zinc cations, sulfate anions, and hydrocyanic acid, said copper containing precipitate comprising copper values, iii) subjecting said zinc loaded anion exchange material to an acidic zinc stripping treatment step for removing zinc values therefrom comprising contacting said zinc loaded anion exchange material with an aqueous acidic zinc eluting solution comprising sulfuric acid so as to obtain an acidic zinc containing eluate and a treated anion exchange material, said acidic zinc containing eluate comprising zinc cations, sulfate anions and hydrocyanic acid, at least a portion of said aqueous acidic solution obtained from step ii) being used in step iii) for removing zinc values from said zinc loaded anion exchange material, iv) gas stripping HCN from at least a portion of said acidic zinc containing eluate obtained from step iii) so as to obtain a HCN laden gas and a stripped aqueous acidic solution comprising zinc cations and sulfate anions, v) adjusting the pH of said stripped aqueous acidic solution obtained from step iv) by admixing, with the stripped aqueous acidic solution, a caustic material capable of forming calcium sulphate and an insoluble heavy metal hydroxide therewith, so as to obtain a product liquor and a product precipitate comprising zinc hydroxide and calcium sulfate, vi) subjecting said product precipitate obtained from step v) to a zinc leaching step comprising contacting said product precipitate with calcium cyanide, in an aqueous liquid medium so as to obtain a remaining product precipitate comprising calcium sulfate and an aqueous alkaline zinc containing solution comprising complex zinc cyanide anions, and vii) recycling complex zinc cyanide anions as obtained from step vi) to said copper stripping treatment step of step i) for removing copper values from said anion exchange material loaded with complex copper cyanide anions.

20. A method as defined in claim 19 wherein product liquor of step v) has a pH of between from about 6 and to about 11.

21. A method as defined in claim 19 wherein product liquor of step v) has a pH of from 8.5 to 9Ø

22. A method as defined in claim 19 wherein the aqueous alkaline zinc containing solution of step vi) has a pH of from 10 to 13Ø

23. A method as defined in claim 19 including a)a precipitate recovery step for separating said aqueous acidic solution from said copper containing precipitate of step ii), before said aqueous acidic solution is subjected to said gas stripping in step iv) and b) a precipitate recovery step for separating said product precipitate from said product liquor of step v) before subjecting said product precipitate to said zinc leaching step vi).

24. A method as defined in claim 19 wherein the HCN laden gas obtained from step iv) is contacted with a caustic substance comprising Ca so as to form calcium cyanide and so obtained calcium cyanide is used in step vi) for obtaining said aqueous alkaline zinc containing solution.