Environmentally friendly method of extracting precious metals from materials containing them

 

(57) Abstract:

The invention relates to metallurgy, and in particular to methods for the recovery of precious metals. The method of extracting precious metals from materials containing them, comprises leaching the material with a solution containing chloride ions, the introduction in the leached solution of sulfuric acid and hydrogen peroxide, the subsequent processing of productive solution with the extraction of precious metals and the return of the recycled solution for leaching. While sulfuric acid and hydrogen peroxide are injected into the leach solution in the form of a mixture, and mixing is carried out by introducing hydrogen peroxide in sulfuric acid at a molar ratio2SO4: H2O2> 1 and cooling. The use of the invention reduces the consumption of reagents and to improve environmental safety and cleanliness of the process. table 1.

The invention relates to metallurgy, and in particular to methods of obtaining noble metals, and can be used to extract gold, silver and platinum group metals from ores, concentrates, slag, a waste, tailings, waste catalysts, electronic scrap, etc.

The known method and the Cl and NO3for example a solution containing 50-350 g/l NCl and 3-50% HNO3at a temperature of 20-110oC. After separation of the metals from the solution of the used solution back into the process (DE 2418441).

The disadvantages of the method is the high consumption of nitric acid, because the efficiency of the process necessary to its high concentration and low environmental safety way due to receive as a waste of nitric oxide.

As a prototype the selected method of extracting precious metals from materials containing them, including the processing of materials circulating washing solution mixture of hydrochloric and sulphuric acids with the addition of hydrogen peroxide and subsequent processing of the productive solution ("Rh, Pt and Pd Recovery from New and Apent Automative Catalysts" // Wu Koo Ying et. al. Precious Metals, 1993, N 17, p. 343-349).

In this way the addition of hydrogen peroxide in a solution of hydrochloric and sulfuric acids will lead to increased consumption of reagents, which also increases the probability of formation and allocation of elemental (gaseous) chlorine in amounts that reduce environmental safety and cleanliness of the process.

The problem solved by the invention is the reduction of reagent consumption and increase environmental security is lagorodnyi metals from materials containing them, comprising leaching the material with a solution containing chloride ions, the introduction of a leaching solution of sulfuric acid and hydrogen peroxide, the subsequent processing of productive solution with the extraction of precious metals and the return of the recycled solution to the leaching sulfuric acid and hydrogen peroxide are injected into the leach solution in the form of a mixture, and mixing is carried out by introducing hydrogen peroxide in sulfuric acid at a molar ratio of H2SO4:H2O2> 1 and cooling.

The invention consists in the following. When introduced into the leaching solution containing chloride ions sulphuric acid, as cold and when heated, produces a mixture of sulfuric and hydrochloric acids by reaction

2Cl-+ H2SO4= SO42-+ 2HCl (1)

The oxidizing action of hydrogen peroxide is described by polyreactive

H2O2+ 2H++ 2e = 2H2O (2)

is the standard redox potential (ORP) which is equal to + 1,776 century

The reaction of dissolution of noble metals such as gold and platinum, with the participation of hydrochloric acid and hydrogen peroxide will be

2A (4)

The standard redox potential dissolution in chloride environment gold (+1,0) and platinum (+0.7 V) is significantly lower than the redox potential of hydrogen peroxide. But really oxidative activity of hydrogen peroxide is manifested only at high pH and a high concentration of hydrogen peroxide and chloride ions in solution. However, if the pre-mix concentrated hydrogen peroxide and sulfuric acid, the proportion of sulfuric acid and hydrogen peroxide to form nadseroy and menandrou acid reactions

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Nadmerna and monongalia acids are much stronger and active oxidants than hydrogen peroxide (ORP = 2,12). Reactions (5, 6) clearly reversible and both nadzornye acids also dissolve upon dilution and elevated temperature, and hydrogen peroxide. However, if a mixture of concentrated hydrogen peroxide and sulfuric acid to cook while cooling within the temperature 0-30oC and apply immediately after cooking, the majority of the hydrogen peroxide turns into menandrou acid.

Besides, what matters is the order of mixing hydrogen peroxide and sulfuric acid. If you enter sulfuric acid to the hydrogen peroxide, when smeII hydrogen, and then to oxygen. The result will be unproductive loss used hydrogen peroxide. If you enter the hydrogen peroxide in sulfuric acid, then nadzornye acid will be diluted sulfuric acid, which increases their stability. In the conversion of peroxide in nadzornye acid will be much more complete. For these same reasons, the molar concentration of sulfuric acid in the finished mixture should not exceed the molar concentration of hydrogen peroxide. In other words, the mixture must contain a molar excess of sulfuric acid in accordance with reaction (6), i.e., must comply with the ratio of H2SO4:H2O2> 1.

When introduced into the leaching solution of hydrogen peroxide in the form of a mixture with sulfuric acid obtained nadzornye acids decompose, but much slower than the hydrogen peroxide. In addition, the hydrogen peroxide decomposes into oxygen and water, and nadzornye acid substantially decomposed by ozone. And if the oxygen in these conditions is not an oxidizer for noble metals, the resulting ozone is an oxidizer, and a stronger and more active than hydrogen peroxide. In the pre-mixing the hydrogen. The consequence of this circumstance is a real opportunity to maintain a much lower concentration of oxidant, acid and chloride ions in the leaching solution, while the dissolution of noble metals. As a result, the consumption will be reduced.

AFP education elementary chlorine is +1,36 in and is between the values of the redox potential of precious metals and hydrogen peroxide. Polyreactive education chlorine is

Cl2+ 2e = 2 CL-(7)

And although from polyreactive (7) it follows that the probability of formation of elemental chlorine depends only on the concentration of the chloride ions, actually it depends on the acidity of the solution. The fact that elemental chlorine hydrolyzed with the formation of hypochlorous acid having the ORP is significantly greater than that of chlorine (+1,63), and high acidity inhibits the hydrolysis and facilitates the oxidation of the chloride ions in elemental chlorine. Therefore, if lead leaching at high pH and concentration of the chloride ions, the probability of formation of elemental chlorine increases. Conversely, at low concentrations of acid and chloride ions, this probability decreases. Thus, the ability to support smaller to the ness formation of elemental chlorine and improves environmental safety and cleanliness of the process.

All injected hydrogen peroxide can be mixed with a part of the entire insertion of sulphuric acid, when the acidity is necessary to maintain relatively high, for example by leaching of platinum. In this case, the other part of the sulfuric acid is introduced into the leach solution before adding the peroxide mixture. In case of the need to maintain low acidity, for example by leaching of the ore of gold, all the peroxide is mixed with the entire insertion sulfuric acid and both reagents are added in the leaching solution only in the form of a mixture. The ratio of hydrogen peroxide and sulfuric acid in the mixture may vary quite widely, depending on the concentrations of these reagents in the initial reagents, as well as from acid and regenerative capacity leached ores and materials. Most importantly, during the preparation of the mixture, and at the end in the finished mixture was ensured molar excess of sulfuric acid. Preferably, the hydrogen peroxide contained in the source reagent in the range of 30-60%, and sulfuric acid is in the range of 92-98%. When the agitation process variant peroxide mixture can be dosed directly into the leach slurry as cold and heat. In the case of heap leaching solution directly before feeding it to the leaching of ores. The source of the chloride ions in the leaching solution can serve as the chlorides of alkali and alkaline earth metals, and hydrochloric acid and aluminum chloride and other chlorides. Processing of production of the solution is carried out by traditional methods: adsorption, electrolysis or by cementation, with the return of the circulating solution by leaching.

On known and proposed options were processed platinum source alumina catalyst leaching solution containing aluminium chloride. Processing of data was performed with stirring on a magnetic stirrer and a temperature of 80oC in sealed glass vessels. The vessels were equipped with devices for dosing reagents and exhaust gases through the valves, filled with a solution of sodium hydroxide and 200 g/l At a known variant concentration in the solution was: Cl - 8M, H2SO42.5 M, 30% hydrogen peroxide was desirables for 1 hour in different numbers counting from 10 to 100 g per 1 kg of catalyst.

On the proposed variant concentrations were: Cl - 2M, H2SO4- 0.5 M Mixture of 30% hydrogen peroxide and 92% sulfuric acid was prepared from the calculation: 1 volume of sulfuric acid and about 1 is SUP>C cooled cooled water. Molar concentration of sulfuric acid in the mixture was -8,6 M, hydrogen peroxide -5 M, that is, the mixture contained a substantial molar excess of sulfuric acid. The resulting mixture was also desirables for 1 hour in different quantities based on hydrogen peroxide from 5 to 15 g per 1 kg of catalyst. At the end of processing both versions of the pulp was filtered off, the solution was determined by the concentration of sulfuric acid and platinum, which were calculated the degree of extraction and the weight of sulfuric acid. In solutions of caustic potash in valves active chlorine was determined and calculated specific yield of chlorine gas during processing. The results are presented in the table.

From the table it follows that on the known variant a high degree of extraction of platinum 93.4% are achieved only when the specific consumption of hydrogen peroxide in 100 g/kg of catalyst and sulfuric acid to 220 g/kg of the specific gaseous chlorine was 14 g/kg For the proposed option is already in the specific consumption of hydrogen peroxide - 10 g/kg and sulfuric acid - 121 g/kg removed 96% of platinum, and the specific gaseous chlorine was only 0.4 g/kg Thus, as h is increased.

The method of extracting precious metals from materials containing them, comprising leaching the material with a solution containing chloride ions, the introduction of a leaching solution of sulfuric acid and hydrogen peroxide, the subsequent processing of productive solution with the extraction of precious metals and the return of the recycled solution for leaching, characterized in that the sulfuric acid and hydrogen peroxide are injected into the leach solution in the form of a mixture, and mixing is carried out by introducing hydrogen peroxide in sulfuric acid at a molar ratio of H2SO4: H2O2> 1 and cooling.

 

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FIELD: noble metal hydrometallurgy.

SUBSTANCE: invention relates to method for acid leaching of platinum method from secondary raw materials, in particular from ceramic support coated with platinum metal film. Target metals are leached with mixture of hydrochloric acid and alkali hypochlorite at mass ratio of OCl-/HCL = 0.22-0.25 and redox potential of 1350-1420 mV.

EFFECT: decreased leaching temperature, reduced cost, improved platinum metal yield.

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