Electrochemical Oxidation Leaching of Gold-Arsenic Concentrates and Sulfide Concentrates 2

In the caustic soda solution, and an electrochemical arsenic pyrite leaching pyrite mechanism is built on the basis of a number of successive stages of the reaction. The electrochemical oxidation is from OH - ions are adsorbed at the start of the sulfide surface. According to the influence of the anion of the solvent on the leaching process of arsenic pyrite and pyrite in alkaline and acidic solutions and the electrochemical properties of oxidation, the adsorption complex formed on the surface of the mineral can cause electrons to be vulcanized. It is easier to transfer the oxidant to the oxidant and promote leaching under the more "moderate" oxidizing conditions.

In the initial stage of sulfur oxidation, after sulfur is transferred to the liquid phase, many compounds are formed with oxygen. However, since the electrolytic cell has an oxidizing medium, the majority of the compounds are present for a short period of time. Depending on the oxidation conditions and oxidation time, 80 to 90% of the sulfur is oxidized to sulfate ions. Arsenic is transferred to the solution in the form of trivalent and pentavalent ions. In the initial stage, the ratio between the trivalent and pentavalent ions is approximately equal, and then most of the arsenic is oxidized to pentavalent.

Studies on the ratio between sulfur and iron have shown that sulfur is preferentially leached when leached more than mild, oxidizing conditions and low temperature leaching. As the potential and temperature of the solution increase, the selectivity of sulfur leaching decreases, while the ratio of sulfur to iron reaches the stoichiometric value of the original mineral. Arsenic also has similar behavior. But arsenic is transferred to the solution at a lower rate than sulfur.

At the beginning of oxidation, the solid phase is a hydroxide of ferrous iron. These hydroxides   Is when they were moved in the positive direction of potential, the adsorption of OH - ions and iron ions in the mineral crystal firmly bonded. In an oxidant conditions, a hydroxide alkaline medium, divalent iron is oxidized to ferric hydroxide, and then converted to more stable compounds Fe 2 O 3.

The electrochemical oxidation process can be illustrated by the following reaction equation:

    2FeAsS+10NaOH+7O 2 =Fe 2 O 3 +2Na 2 SO 4 +2Na 3 AsO 4 +5H 2 O ,

    2FeS 2 +8 NaOH + 7.5O 2 = Fe 2 O 3 + 4Na 2 SO 4 + 4H 2 O .

At this time, in addition to sodium sulfate, there are sodium sulfite Na2S03 , sodium thiosulfate Na 2 SO 2 , and other compound Nan ( SxOy ). In the arsenic pyrite leaching process, sodium arsenite NaAsO 2 is also formed simultaneously with sodium arsenate Na 3 AsO 4 . In the process, a reaction capable of generating iron sulfate and magnetite also occurred. However, the yield of these reactions the resulting product - as no more than 2 to 5%.

According to the data on the kinetics and mechanism of the electrochemical oxidation process of arsenic pyrite and pyrite, when the caustic soda concentration is 2.5~ 3.75 grams Molecular / liter and solution temperature is not less than 50~ 60 °C Both minerals have the best leaching speed. In actual concentrates, the leaching speed of the two minerals depends on the structure of the cell, the oxygen required per unit volume of solution, the current density of the anode, the particle size characteristics of the material, and the composition of the suspension.

Electrochemical leaching of three gold - arsenic concentrates with different levels of arsenic pyrite and pyrite was studied. The results show that - very good method (see flow chart). Under the optimal conditions, the oxidation of this concentrate can make the leaching of arsenic pyrite up to 72~87% and the leaching rate of pyrite is 45~53% . Therefore, the gold crystal position in the tailings after cyanidation is substantially the same as the gold grade of the tailings when the concentrate is processed according to the roasting - baking cyanidation process.

After removal of arsenic and sulfur, the electrochemical leachate can be returned to use without degrading its process specifications. When the solution is treated with lime, the arsenic is slightly soluble in the form of arsenic acid: calcium, and the solution is concentrated by caustic soda. 150 grams / Liter and cool to 16~ 17 °C Thereafter, the sulfur is removed as anhydrous sodium sulfate. Thus, gold - Concentrate study electrochemical oxidation of arsenic leaching process, and technical testing - evaluation results justify this economic - feeding method - test expansion step, and in a variety of non-ferrous metals processing arsenopyrite containing impurities When mineral processing products are used, it is possible to use mineral beneficiation methods to achieve mineral sorting.

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