Biotechnology

As near-surface oxide orebodies are depleted, mines are having to process deeper sulfide ores that are lower in metal grade and metallurgically more complex. Modern technologies that are simple, cost effective and environmentally sound are required for their extraction. In many cases, bioleaching is the most suitable process.

About Biotechnology

Introduction

The Biotechnology Division of Mintek deals with the processes of living organisms, or matter derived from living organisms which can bring about chemical and physical reactions applicable to the beneficiation of minerals.

In general, value is derived from minerals via the steps of exploration, mining, size-reduction (i.e. crushing or milling of rocks), extraction and separation/purification/recovery to yield a saleable product from which semi-finished and finished goods are manufactured. Biotechnology has mostly been applied to the extraction step, but also has contributions to make to the mining, size-reduction and separation/purification/recovery steps. Biotechnology also has the potential for playing an increasing future role in the treatment of the effluents of minerals processing plants and of metals-bearing wastes.

Biotechnology offers certain unique features, which makes it well suited to a number of the processes required in the exploitation of minerals. A well-known example is the ability of certain bacteria to oxidise ferrous iron (to generate ferric iron as an oxidant), and to oxidise elemental sulfur to generate acid, under much milder conditions than would be required to conduct the same reactions in the absence of the bacteria. This is the result of the biochemical routes according to which the bacteria utilise iron and sulphur in their life processes, catalysed by enzymes.

Mintek’s Biotechnology Division has been involved in the application of these biological reactions to the processing of minerals since the early 1980s. A number of processes have progressed from the laboratory to become piloted, demonstrated and commercially applied.

The activities undertaken by the Biotechnology Division include the small-scale testing of ores and concentrate samples to verify their amenability to bio-treatment, the generation of flow diagrams for the conceptualisation of complete processes, and estimation of the economics of such processes.

Much of the commercial activity involves conventional heap leaching test work, geomechanical testing of crushed ore for heap leaching, as well as more developmental test work involving high-temperature heap bioleaching, research into the gangue chemistry of heap leaching, and the modelling and simulation of the chemical and physical processes of heap leaching.

The Division also undertakes research in new bioprocessing applications for the treatment of wastes and effluents.

Overview

Two commercial gold bioleaching plants have been built and operated using Mintek’s Bacox™ technology, the first at the Tasmania Mine (formerly the Beaconsfield Gold Mine) in Tasmania, Australia in 1999, and another in 2001 at the Shandong Tiancheng Biotechnology Gold Industry facility (formerly the Shandong Tarzan BioGold facility) in Laizhou, Shandong Province, PR China. In this process bioleaching is used to remove pyrite, which occludes the gold, so that the gold becomes extractable by the conventional cyanidation process.

A process was demonstrated for the bioleaching of copper from chalcopyrite concentrate contaminated with zinc, lead and other elements, including the production of commercial size A-grade cathodes. In most other processes the high concentration of lead will interfere with the copper extraction, but the bioleach process permits a window of operating parameters which overcomes that problem. The process can also be applied to most other base metal sulfide concentrates.

As part of the BioMinE project under the Sixth Framework Programme funded by the European Union, a similar process has been tested in closed circuit with downstream precipitation for the recovery of nickel from pentlandite concentrate. As part of the same programme, the use of extreme-temperature microbes in the bioleaching of chalcopyrite concentrate was refined.

The Division is at the forefront of high-temperature heap bioleaching, having designed, built and operated a number of 20,000 tonne high-temperature pilot heaps at high altitude. In the run-up to the development of that technology, it was necessary first to develop a number of other innovations, such as a set of in-heap instruments, heap leach administration and guidance software (HeapStar®), as well as the SmartColumn® for simulating the centre of a heat-generating heap.

The Division operates as an integral part of the mineral processing, mineralogical and analytical and other capabilities of Mintek. Specifically the investigations on minerals-related wastes and effluents are conducted in collaboration with the Hydrometallurgy Division and the accredited Cyanide Centre of Mintek.