Effluents Treatment Generated by Biolixiviation in the Extraction of Precious Metals through Selective Recovery of Iron, Copper and Zinc

Zambrano Johanna,Zambrano Johnny

doi:10.11648/j.ijmpem.20190402.12

Abstract

Bioleaching comprises the use of microorganisms for metal-extraction processes from sulphide ores. During these complex processes, sulphides are oxidized to sulphates with the generation of heat. As a result, gold, silver, and other precious metals are liberated from the sulphide matrix, improving their recovery after further processing. A drawback of bioleaching processes is the generation of significant amounts of acid solutions with high heavy metal concentrations. If untreated, these acid solutions may alter the physical and chemical characteristics of water and its surroundings, with high impact to aquatic ecosystems. High heavy metal concentrations in solution may also result in pollution to living organisms. A feasible method to treat bioleaching-generated solutions is selective precipitation. This investigation presents the conditions for a successful individual recovery of the main base metals contained in a bioleaching solution with high copper, zinc, and iron concentrations by pH-based selective precipitation. Tests were made with standard solutions of known concentrations of copper, iron, lead and zinc and by titration the concentrations were checked; which allowed to validate the volumetric titration method. The selective precipitation of heavy metals was carried out in three phases using real acid main drainage and bioleaching solutions generated at the laboratory. The first phase in a pH range of 2 to 4 to recover iron; the second phase in a pH range of 4 to 6 to recover copper; and the third phase in a pH range of 6 to 10 to recover zinc. The selective precipitation allowed the heavy metals to be completely removed from the solution or to achieve concentrations below the maximum allowable limit to be discharged to a body of water or public sewer. Results portray that the variation of pH is an effective method, easy to use and not expensive, feasible to be used in the purification of waters that have been polluted with heavy metals.

Highlights

In Ecuador, large gold mining deposits have been discovered in the areas of Nambija and Ponce Enríquez, in addition to traditional mining activities in Zaruma and Portovelo areas [1]
From the exploitation of these deposits, artisanal and industrial mining activity is developed in the south of the country, generating large investments, especially from foreign countries, and changes in mining legislation [2,3,4]
The aim of this study is to use selective precipitation, in order to recover iron, copper and zinc from acid solutions produced by bioleaching during the extraction of precious metals at a laboratory scale and from natural acid mine drainage, which will allow to comply with environmental regulations regarding to effluents discharge and to decrease the effect of environmental pollution generated by acid mine drainage [13, 14]

Summary

Introduction

In Ecuador, large gold mining deposits have been discovered in the areas of Nambija and Ponce Enríquez, in addition to traditional mining activities in Zaruma and Portovelo areas [1]. From the exploitation of these deposits, artisanal and industrial mining activity is developed in the south of the country, generating large investments, especially from foreign countries, and changes in mining legislation [2,3,4]. In these mining districts, the gold deposits contain metal sulfides such as pyrite, chalcopyrite, arsenopyrite, galena and sphalerite, and when exposed to the action of air and water they undergo throw a series of physical, chemical and biological phenomena. These solutions, with a high level of acidity, pH around 2, are dragged by water currents or runoff, constituting a powerful water and soil pollutant [6]

Objectives

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Results

Conclusion