FIELD OF THE INVENTION The present invention pertains to a method for the recovery of base metals such as cobalt, nickel, copper, lead, zinc, mercury and cadmium, precious metals such as silver and gold, as well as the platinum group metals, comprising ruthenium, rhodium, palladium, osmium, iridium and platinum, from fresh ore, mine tailings and industrial wastes.

BACKGROUND OF THE INVENTION Base metals, precious metals and the platinum group metals (PGM), are used in a broad spectrum of industrial applications. Their extraction or recovery is therefore of major importance.

It is quite frequent to find several of these base or precious metals, in a specific ore body. For example, gold is often found in variable amounts in association with copper or zinc. The presence of silver in some zinc or lead minerals has been known since earliest mining operations. There are quite often significant amounts of chromium and/or nickel or copper associated with the PGM bearing ores. Therefore, the recovery of more than one metal in a single operation is of interest. However, with many existing extraction procedures, the presence of one metal may prevent a smooth extraction of another one, as is observed in the case of gold extraction with cyanide, while in the presence of silver or copper.

The tailings from the mining of these complex ores, especially from the old sites, may contain significant amounts of either base or precious metals. A similar situation prevails to some extent with complex industrial metallic wastes, which may contain significant amounts of the platinum group metals.

The composition of the ashes, resulting from the incineration of wastewater muds of the city of Toronto (Canada), is an example of such a complex industrial waste. The composition was shown to contain 350 g/T of silver, 4 g/T of gold, 0.64 g/T of platinum, 0.5 g/T of palladium and 0.29 % of copper.

These values resemble more the numbers expected from the analysis of a high quality ore, rather than a waste material.

Because of the diversity in physical and chemical properties of base, precious metals and PGM metals, there does not exist a common procedure, allowing for the recovery of most, if not all, of these metals in a single operation. As a result, a large number of methods are currently used in the recovery of these metals. Ever since the oxidation of sulfides has been abandoned for environmental reasons, metals such as nickel and cobalt are leached by agent, taking advantage of their propensity to complexation. Gold is generally collected through cyanide extraction. Lead and zinc sulfides continue to be roasted, wherein the liberated S02 is being used in the manufacturing of sulfuric acid. The same situation applies to mercury. Copper is either obtained by heap leaching with sulfuric acid or obtained through smelting and electro- refining. Finally, the PGM are obtained through a very complex series of pyrometallurgical processes, involving the associated metals comprising copper, nickel, cobalt and chromium. These methods are generally quite specific, being useful only in the recovery of at most one or a few of the metals in one basic operation.

OBJECT AND STATEMENT OF THE INVENTION It is an object of the present invention to provide a method for the recovery of base metals (Co, Ni, Cu, Zn, Cd, Pb, Hg), precious metals (Ag, Au) and platinum group metals (Ru, Rh, Pd, Os, Ir, Pt) from fresh ore, mine tailings and industrial wastes, in one type of operation. The interest for such a procedure stems from the composition of some ores, certain mine tailings and industrial wastes, where several of the above listed metals are present.

This is achieved by a method, which consists of a series of steps including: (a) analyzing the ore, mine tailings or industrial wastes to determine the presence of one or more of the above mentioned metals ; (b) chloridating the ore with a strength determined by the presence of the most refractory of the metals ascertained by the analyzing step, in the presence of a source of chloride ions in an amount determined by the metals present, to form a solution of metal chlorides and a sterile residue; (c) separating the solution of metal chlorides from the residue to produce a filtered solution of metal chlorides ; (d) recovering the metal chlorides from the filtered solution of metal chlorides to produce a barren solution; and (e) recycling the source of chloride ions.

The combination of these metals with different low-cost cations, as for example sulfates, phosphates and chlorides, leads in many instances to the formation of insoluble species. In the case of the formation of chlorides however, it was observed that the corresponding solubilities are directly

related to the ionic strength of the solutions in chloride ions. This situation is readily understood by examining the solubility of the chlorides of Cu+, Ag+, H922+ and Ir3+. These metallic chlorides are either water insoluble or of very low water solubility. It was experimentally observed, however, that when the chloride ion concentration in the solution is raised to an appropriate level by the addition of, for example a chloride such as sodium chloride, then the solubility of the less soluble metal chlorides is substantially increased.

With the implementation of a chloridation process able to generate the corresponding chlorides of the metallic species to be reclaimed, namely base metals, precious metals and platinum group metals (commonly found in complex ores, mine tailings or industrial wastes), it will then be possible to simultaneously solubilize these chlorides if the chloride ionic strength is at the appropriate level. With this procedure, the metallic species, present either in the form of a free metal, an oxide, a silicate, a carbonate, a sulfide, an arsenosulfide or a polysulfide, will be transformed into a soluble chloride, if the ionic strength in chloride ions is at a sufficient level.

The ionic strength requirement in chloride ions, necessary to achieve solubility, will vary from metal to metal and will consequently be directly dependent on the requirements in chloride ion by the least soluble of the metal chlorides in a given mixture of metals.

It was determined that, by adjusting the conditions of the chloridation procedure and by adjusting the ionic strength of the chloride ions in solution, all base metals, precious metals (including PGM) along with mixtures of both types of metals could be reclaimed.

Unless defined otherwise, the scientific and technological terms and nomenclature used herein have the same meaning as commonly understood by a person of ordinary skill. Generally, procedures such as recovering a-or more compounds from a reaction mixture are common methods used in the art. Such standard techniques can be found in reference manuals such as for example Gordon and Ford (The Chemist's Companion: A Handbook of Practical Data, Techniques and References, John Wiley & Sons, New York, NY, 1972).

The present description refers to a number of routinely used chemical terms.

Nevertheless definitions of selected examples of such terms are provided for clarity and consistency.

As used herein, the terminology"recovering"a desired compound or compounds or the like, well known in the art, refers to such a desired compound or compounds or the like having been isolated from other components of a reaction mixture.

As used herein, the terminology"concentrated"well known in the art, refers to an acidic solution having a concentration equal to or higher than 15%.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram illustrating the various steps of one embodiment of the method according to the present invention; Figure 2 is a block diagram illustrating the various steps of a second embodiment of the method according to the present invention; and Figure 3 is a block diagram illustrating the various steps of a third embodiment of the method according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The conditions of chloridation vary with different metals, being as low as 100°C for nickel oxide and as high as 600 °C for the platinum group metals.

While doing the chloridation, it is necessary to have the source of chloride ions, normally sodium chloride, present in the reaction mixture so as to have available in situ the chloride ion concentration required for the solubilisation at the time of leaching, upon completion of the chloridation step. Sodium chloride is used but potassium chloride or calcium chloride can also be used.

The energy required to achieve chloridation will vary with the chemical reactivity of the metal or group of metals under consideration. To maintain the energy consumption at a minimum and taking into consideration the solubility characteristics of each metal, three levels of chloridation ability have been developed.

Low temperature (40-50 °C) chloridation with chlorine in the presence of a near saturated solution of sodium chloride is appropriate for metals such as

Cu, Ag, Au, Cd, Hg, and Pb, these metals showing a rather high reactivity but giving in some instances chlorides of very low solubilities. High temperature (500-600 °C) chloridation with chlorine in the presence of a source of chloride ions, such as solid NaCI, KCI or Cal2, (approximately 5% by weight) is required mainly for PGM. Chloridation using hydrochloric acid at a temperature near 100 °C, is appropriate for base metals, particularly when iron is present.

The selection of one of these methods allows for the recovery of the metal values from most combinations found either in nature or in antropogenic wastes.

In the case of chloridation with chlorine at (40-50 °C), the operation is conducted in a near saturated solution of either NaCI, KCI or CaCl2 and the precious metals are readily recovered over activated carbon, while the residual base metals are obtained by electrolysis, leaving behind a barren solution. The near saturated salt solution is then recycled for further operation.

In the case of high temperature chloridation, upon completion of the chloridation step in the presence of approximately 5% by weight of solid NaCI, KCI or CaC12, the dry mixture is leached with concentrated hydrochloric acid (-15%) so as to extract the soluble metal chloride species from the sterile residual materials. This is followed by a filtration step in order to separate the solution of metal chlorides from the sterile residual materials. Since chlorine is an oxidant, the chloridation process at 500-600 OC constitutes a strong oxidation reaction. The metal chlorides will therefore be in solution at their maximum valency. To obtain the free metals in reduced state, a variety of

methods are available. However, the selection of these methods must take into account the very strong dissolving power of the chloride-rich acid solution.

Therefore, in order to avoid incomplete recovery or redissolution of the desired metals, the following procedure was found to be very efficient.

Circulating the acid solution obtained after chloridation with chlorine and leaching with concentrated HCI over a bed of activated carbon, results in the retention of all the platinum group metals and all of the gold. The base metals can be extracted by electrolysis. The remaining so-called barren solution is recycled allowing for the recovery of the source of chloride ions and concentrated HCI, for further operation.

In the case of hydrochloric acid leaching, applied to a mixture of base metals, the substrate may contain substantial amounts of iron in the form of sulfides (pyrites, etc...), oxides (limonites, etc...) or metallic iron. The chloridation will transform part of this iron into ferric chloride and in doing so, will consume significant amounts of chlorine. In order to recover this chlorine fixed on iron, the acid solution of ferric chloride and other metallic chlorides is evaporated and heated at temperatures of 200-250 OC while in the presence of moisture.

Under such conditions the ferric chloride is subjected to hydrolysis, resulting in its transformation to ferric oxide with the concomitant liberation of HCI as is shown by the following equation: It is important to note that the remaining metal chlorides present in the mixture, namely, Nicol2, CoCl2, CuCl2, PbCl2, AgCI, ZnC12, HgCl2 and CdCI2

are not affected by this mild hydrolysis. All of these chlorides can be separated from the ferric oxide by leaching with water. They can then be individually separated and isolated by techniques such as selective electrolysis (Cu, Ni, Co) and selective sulfide or pH adjustment precipitations, techniques well known by those familiar in the art.

The recovery of metal values by either low or high temperature chloridation, results in the formation of a barren solution containing the source of chloride ion (NaCI, KCI or Cal2). This barren solution is acidic in nature due to the presence of hydrochloric acid, resulting from the dissolution of chlorine gas according to the following equation: In the case of low temperature chloridation, approximately 99% of the barren solution is recycled to the chloridation step whereas about 1% is subjected to electrolysis. Chlorine gas is produced in the course of the electrolysis and is recycled to the chloridation step as well. Furthermore, during the electrolytic procedure, sodium hydroxide (NaOH) is generated, in equimolar amounts to chlorine gas. The sodium hydroxide is collected and used to treat the barren solution upon completion of the recovery of the metal values.

In the case of high temperature chloridation, approximately 99% of the barren solution is recycled to the chloridation step and wherein HCI is produced which is recycled to the lixiviation step. Approximately 1% of the barren solution is subjected to electrolysis, resulting in the production of chlorine gas that is also recycled to the chloridation step. As was previously mentioned, the electrolytic procedure leads to the formation of sodium hydroxide (NaOH), in

equimolar amounts to the generated chlorine gas. As was the case for the low temperature chloridation, the sodium hydroxide is collected and used to treat the barren solution upon completion of the recovery of the metal values.

These different operations are illustrated in Figures 1-3 of the present application.

As mentioned previously, the presence of a high chloride concentration is a basic requirement for the implementation of the invention. It has been established that the chloridation of Au and Ag using chlorine gas could be carried out at low temperatures (30-50 °C) when in the presence of a near saturated solution of sodium chloride. It is noted that near saturated solutions of potassium chloride or calcium chloride are also effective. In the case of the platinoids, however, the chloridation with chlorine gas must be performed at temperatures ranging from 500-600 OC while in the presence of a solid source of chloride ions, achieved by the addition of about 5% by weight of sodium chloride. It is also noted that the solid source of chloride ions can also be potassium chloride or calcium chloride, used in the same proportions. This chloridation procedure is followed by a lixiviation step using hydrochloric acid.

In the case of the base metals (Cu, Ni, Co, Zn, Pb, Fe), the chloridation procedure can be effected with hydrochloric acid. With both types of chloridation (Ci2 or HCI), the main group metals (Cd, Hg, Pb) will be lixiviated when in the presence of a strong chloride concentration such as for example a near saturated sodium chloride solution.

The operation of the system calls for a closed circuit approach, more specifically:

1. The near saturated solution of NaCI, KCI or CaC12 in the low temperature chloridation procedure, is recycled to the system after removal of the leached metal values by activated carbon (Au, Ag) and electrolysis (Cu, Ag, Cd, Hg, Pb).

2. The high temperature chloridation gives a leach in concentrated hydrochloric acid. The hydrochloric acid is recycled after removal of the metal values (mainly the platinum group metals) by electrolysis, by activated carbon or by specific ion exchange resins under acidic conditions.

3. The hydrochloric acid used in the chloridation of the base metals is recycled by the mild thermal treatment of ferric chloride.

The chloridation process while in the presence of a high concentration of chloride ions, offers flexible avenues to the low cost extraction of a wide variety of metals, such as base metals, platinum group metals and precious metals. The strength of the reagents (C12 or HCI) and the operating temperatures (40-50 °C or 500-600 °C) are adaptable to the sample at hand and hence the combination of metals to be recovered.

EXAMPLES EXAMPLE 1 Recovery of the metallic values present in the ashes resulting from the incineration of wastewater sludges.

Municipal wastewaters carry significant amounts of organic matter in suspension. These waters are therefore first flocculated and filtered before

treatment. Accordingly, the city of Toronto (Canada), uses ferrous chloride as a flocculating agent in the treatment of its wastewaters. The solid obtained after filtration is incinerated, so as to reduce its volume and eliminate bio-toxic elements. The resulting ashes revealed the following composition: Au: 4.01 g/T; Ag: 5.05 g/T; Pt: 0.64 g/T; Pd: 0.51 g/T; Fe: 21.7%; Cu: 0.29%; Zn: 0.23%; Ni: 0.011%. Monthly samples of this material displayed maximum variations of 5% over a 1-year period. This material was submitted to high temperature chloridation.

A 50.0 g sample of ashes was placed in a tubing, known under the trademark Vycor, after being well mixed with a 4.0 g sample of sodium chloride. The sample was then heated in an electric furnace for 4 hours at a temperature of 575 °C. During this heat treatment, a slow stream of nitrogen (20 ml/min), charged with chlorine gas, was circulated through the Vycor tube. The chlorine gas was generated via the electrolysis of a solution of sodium chloride (35.0 g) in 15 % HCI (250 ml). The nitrogen stream first vented the anodic compartment before reaching the reaction tube (current of 5.0 amp, 4.5 volts, anode of graphite). Approximately 0.35 moles of chlorine gas were produced. After contacting the sample with the so produced chlorine gas, the sample was cooled and extracted with 15% HCI (150 mi) and heated to approximately 100 °C for one hour. The reaction mixture was then filtered, to produce an acidic solution of metal chlorides and a residue. The solid residue, while wet, was taken up with a saturated NaCI solution (200 ml) and heated at 100 OC for one hour and filtered and rinsed with two 20 mi portions of a saturated NaCI solution. The acid solution and the salt solution were then analyzed for their metal content. The ashes were analyzed for any residual metal values. The acid solution was revealed to contain 97% of the gold, 12%

of the silver, 98% of the platinum, 99% of the palladium, 12% of the iron, 96% of the copper, 85% of the zinc and 92% of the nickel present in the initial ashes. The sodium chloride rinsings contained 84% of the initial amount of silver. Contacting the acid solution with activated carbon (25 g; Norit A) resulted in the removal of Au, Pt and Pd below detectable level (0.001 ppm).

After removal of the precious metals by activated carbon, the acidic solution was evaporated to dryness and the resulting solid heated up to 250 °C. The hydrochloric acid produced in the heating process was collected and recycled.

The residual solid was rinsed with water and the extracted base metals (in the present example copper chloride) collected as sulfides.

EXAMPLE 2 Recovery of gold, silver and mercury A 50 g sample of mine tailings from the Pedernalillo mine in the Province of Zacateca (Mexico), containing Au: 2.4 g/T; Ag: 91.1 g/T and Hg: 0.7 g/T, was suspended while stirring in a solution of sodium chloride (170 g) in water (500 ml). The suspension was maintained with a mechanical stirrer and saturated with chlorine gas. The temperature was maintained with a water bath kept at 40 °C. After chloridating for two hours, the suspension was filtered and the solid residue rinsed with two 20 ml portions of a saturated NaCI solution. The combined filtrate and rinsings were then contacted with activated carbon (10 g) over a period of one hour and the carbon filtered and dried. A subsequent analysis of the carbon and residual solution indicated that 96% of the gold and 75% of the silver initially present in the tailings were collected on the carbon.

The residual solution was submitted to electrolysis (2.0 V, 1.0 amp.) using a

copper cathode. After 15 minutes, all of the mercury and all of the residual silver were deposited on the cathode.

EXAMPLE 3 Recovery of silver and lead.

A 50 g sample of ore from the Pachuca mine, located in the Province of Hidalgo (Mexico) containing Pb: 0.9% and Ag 42 g/T was treated in a manner similar to Example 2. The suspension, after chloridating for 2 hours at 40 °C, was filtered, rinsed and submitted to electrolysis. 99% of the initial Pb and 96% of the initial Ag were collected on a copper cathode. At the graphite anode, the evolution of chlorine gas was noted, which was subsequently recycled for further reaction, as was the solution deprived of Ag and Pb.

Although the invention has been described above with respect to three specific embodiments, it will be evident to a person skilled in the art that it may be modified and refined in various ways. It is therefore wished to have it understood that the present invention should not be limited in scope, except by the terms of the following claims.