The Research and Application of Two Step Precipitation for Barren Solution Purification

1. Brief Introduction:
Two step precipitation is for the purpose to solve the problem of the continuous accumulation of heavy metals that causes the leaching ratio of gold to decrease when the barren solution is circulatively used. The technique of barren solution purification jointly developed by Changchun Gold Research Institute and Penglai Gold Smelting Plant belongs to environment treatment science in the category of environment protection science, involving hydrometallurgical area. This method is based on chemical precipitation theory. According to different states of metal complex with cyanide under different PH value in the barren solution, vitrol is added to adjust its PH value to be equal or below 2, under which condition, the heavy metals are separated by precipitation in the form of cuprous rhodanide and metal cyanide comples to have the barren solution to be purified. Through neutralization reaction, lime is added to the settled acid solution to nuetrlize the vitrol under a PH value of 10~11, forming calcium sulphate, and being re-separated and re-precipitated. At the same time the cyanide in the barren solution was keept, and the purified barren solution is sent back to the cyanidation plant for recycle.

2. Techno-economical Indices and Benefits
The practice shows that the two step precipitation method for barren solution purification achieved good results. The operatioanal indices are that the copper content in the barren solution after purification was ≤86mg/l, which was sent back to the cyanidation section for recycle. The leaching recovery was not only not influenced but also increased somewhat. In eight months of production 15,698 cubic meters of barren solution was treated, with 39.2 tons of sodium cyanide and 54.9 tons of cuprous rhodanide being recovered, which created profit of 660,000 yuan. Deducted the operation cost of 155,000 yuan, a total profit of 505,000 yuan was created.

3. Application Prospects

The method of two step precipitation for barren solution purification realized the target to have the barren solution fully recycled, and achieved “zero disposal” of the syanide-containing waste water, which solve the environment protection problems of gold smelting plant from its fundaments, at the same time enhanced the technical level in complete treatment of the cyanide-containing waste water. This technique can be widely applied in all the gold mines that use cyanidation technique for gold extraction, and it is especially suitable for process renovation of acid recovery technique. It has a promising application future.