Sulfuric Acid Baking—Water Leaching for Gold Enrichment and Arsenic Removal from Gold Concentrate

Bongju Kim,Chulhyun Park,Nagchoul Choi,Soonjae Lee,Jaehyun Kim,Kanghee Cho

doi:10.3390/min11121332

Bongju Kim, Chulhyun Park + Show 4 more

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https://doi.org/10.3390/min11121332

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Abstract

During the roasting of gold concentrate to improve gold recovery, arsenic is released into the air and valuable elements such as Fe, Cu, Zn, and Pb are converted into oxide minerals. In this research, we evaluated the release of As and the loss of valuable metals during the acid baking and hot water leaching processes used for gold concentrate. The acid bake tests were conducted for gold concentrate using an electric furnace by applying various concentrations of H2SO4 solution under different baking times. The water leaching process was enacted using 70 °C water for the baked samples. Chemical and mineral compositions of the raw and treated samples were analyzed using AAS and XRD, respectively. The results show that soluble metal sulfates, such as rhomboclase and mikasite, were formed in the baked samples, and that the leaching of valuable metals (Fe, Cu, Zn, and Pb) was accelerated during the hot water leaching procedure. During acid baking, arsenic was partially removed by volatilization, and the rest of the arsenic-containing minerals were converted to soluble minerals. The soluble arsenic-containing mineral resulted in a dissolution that was 60 times higher than in the roasted sample. The maximum gold grade of solid residues increased up to 33% through the acid baking–water leaching process. It was confirmed that acid baking with H2SO4 prevented As release into the air, as well as the recovery of valuable metals through hot water leaching, such as Fe, Cu, Zn, and Pb, which were formerly discarded in the tailings.

Highlights

Gold is mainly contained in pyrite (FeS2) and arsenopyrite (FeAsS)
H2SO4 was added to gold concentrate, and baking experiments were conducted at a relatively low temperature in an electric furnace
Rhomboclase and mikasite were produced in the soluble baking sample, which was verified through X-ray powder diffraction (XRD)

Summary

Introduction

Since gold contained in pyrite and arsenopyrite is small, smaller than a few microns, it is difficult to observe it with an optical microscope or even with an electron microscope. This gold is called invisible gold, and it is notoriously difficult to liberate it from sulfide mineral. The reason for this difficulty is because invisible gold typically forms a solid solution with sulfide minerals or is chemically bound with sulfides [1] To overcome this problem, the roasting of pyrite or arsenopyrite containing invisible gold, at a high temperature, is a commonly used method [1,2]. It is challenging to achieve dead roasting where S and As are completely removed in the air [6]

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