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Biotechnology 

 
Author: Jack Caldwell

Summary

This review describes the technical and engineering aspects of biotechnology in mining, including mineral processing and ore extraction. Also described are the role of bacterial and biotechnology processes in acid rock and acid mine drainage, leaching of base metals, groundwater remediation, contaminant treatment, and heap leaching.

INTRODUCTION

Biotechnology is the use of living organisms or their products for commercial purposes. Biotechnology has many potential applications in the mining industry including metal leaching, metal recovery, impurity removal and product upgrading, treatment of acid rock drainage and other uses for environmental control.

Commercial applications include processing of refractory gold concentrates to release gold for conventional recovery and the bioleaching of copper in heap and dump leach operations. Commercial application of stirred tank bioleaching for the recovery of copper has also developed rapidly in recent years with the installation of very large bioreactors.

BACKGROUND

Much of this review is from materials on an InfoMine site called BioMetMine. You can access the old site via the link but be warned: the site has sadly not been updated in a while. Todd Harvey and Shannon Shaw have gone on to other things and do not have the time in this period of booming mining sales. Lest we loose their past valuable materials, I have posted what I can in the InfoMine library and collated the remainder in this review. You may prefer their materials, listed and linked here:

Of course there are many other sites that postdate the last update of BioMetMine. One is Microbial Life and their page on Microbial Mining with lots of fascinating links. From the Vellore Institute of Technology in India is an overview article by Devasia and Natarjan on bacterial leaching. Idaho National Laboratory has a page on biomining and bioprocessing and the page links to a number of valuable articles.

You can also find 12 papers in the InfoMine library on biotechnology.


HISTORY

The earliest use of biological systems by the metallurgical industry was in the leaching of uranium in the 1950's. In the1980's bioleaching was used to treat refractory gold ores. Recently commercial processes have been developed for leaching base metal sulphides such as copper, zinc, nickel, and cobalt. Cyanide destruction using bacterial processes was pioneered in Lead, South Dakota at the Homestake Mine.

DEFINITIONS

Although the terms bioleaching and bio-oxidation are often used interchangeably, there are distinct technical differences between these process technologies.

Bioleaching refers to the use of bacteria, principally Thiobacillus ferrooxidans, Leptospirillum ferrooxidans, and thermophilic species of Sulfobacillus, Acidianus and Sulfolobus, to leach a metal of value such as copper, zinc, uranium, nickel and cobalt from a sulphide mineral. Bioleaching places the metal values of interest in the solution phase during oxidation. These solutions are handled for maximum metal recovery and the solid residue is discarded.

Irrigation style bioleaching. (Photo credit: Science Creative Quarterly)

Bio-oxidation refers to a pretreatment process that uses the same bacteria as bioleaching to catalyze the degradation of mineral sulphides, usually pyrite or arsenopyrite, which host or occlude gold, silver or both. Bio-oxidation leaves the metal values in the solid phase and the solution is discarded.


WHAT IS BIOREMEDIATION?

Commercial applications of bioremediation in the mining environment involve the immobilization and recovery of soluble metals from aqueous wastes and the microbial degradation of cyanide species. The types of bacteria vary widely but can broadly be classified as either oxidizing or reducing. The process can take place both in situ by injecting bacteria into the groundwater contamination or externally by pumping the contaminants to a treatment facility. The external system generally has higher capital costs but tends to provide much more rapid treatment.


TYPES OF BIOTECHNOLOGIES

Whole Ore Leaching:

Heap Leach Pads at Newmont's Carlin Operations. (Photo credit: bettermines.org)
  • Heap leach for refractory gold treatment - Newmont, GeoBiotics
  • Heap leach for base metal sulphide recovery

Concentrate Leaching Process:

  • Stirred tank bio-oxidation for refractory gold treatment
  • Stirred tank bio-oxidation for base metal sulphide extraction
  • Heap leach for refractory gold treatment
  • Heap leach for base refractory gold treatment

Water Purification:

  • Cyanide destruction processes
  • Heavy metal removal
  • Nitrate removal
  • Hydrocarbon removal

BIOLEACHING TECHNOLOGIES

WHOLE ORE PROCESSES
In Situ Bioleaching. In situ treatment refers to the process of treating ore without mining in order to remove rock to a treatment process on the surface. This process relies on fracturing the ore by blasting or natural processes, thus producing voids and porosity to allow solution to flow freely. The solution is collected, generally at the bottom of the mine and processed for metals recovery. The biological system receives its oxygen from the solution. The application of this process has not spread widely as it requires very specific orebody characteristics, high permeability ore with low permeability host rock. Additionally, the recoveries are typically low and the time required is long.

Ex Situ. Stirred tank bioleaching - Bacterial oxidation of ground mineral slurry can be carried out in aerated agitated vessels if the value of the metal is sufficient to justify the cost of installing and operating the equipment. The reaction vessel can be either a mechanically stirred tank with a means of introducing oxygen into the slurry or an air agitated Pachuca reactor where the introduction of the air provides not only the oxygen but the agitation of the slurry. The application of this process to ores has been fairly limited due to the large size of the vessels, thus often making its cost prohibitive. However, oxidation kinetics is much higher than in situ or heap systems.

A stacker distributes coated support rock in a heap on an impervious pad.

Bio-oxidation heaps - Heaps are formed by stacking crushed rock into constructed piles on prepared impervious pads that have a sloped base to allow solution to flow by gravity into collection drains. Oxygen can be added to the system to enhance the rate of oxidation by blowing low pressure air into the heap base.

Acidic solutions carry away bio-oxidized products such as copper or iron. Recent advances in whole ore heap leaching have seen the use of closely sized ore particles to aid the oxidation rate, under heap piping for better air distribution and agglomeration, and pre-inoculation to aid in permeability and oxidation rate. Additionally, whole ore systems are now applied to a wide range of ore types including refractory gold ores, copper sulphides, nickel sulphides, cobaltiferrous ores and zinc sulphides.

Vats - Vat leaching refers to a method of treatment in which a sulphide mineral is immersed in solution for all or part of the treatment process. This is a hybrid process that combines whole heap leaching and stirred tank. The vats provide better control of the bio-oxidation environment while not requiring expensive agitation and air distribution. This system is not commonly employed as the bio-oxidation rate is often slow and the extent of bio-oxidation low.

CONCENTRATE PROCESSES
Industrial bioleaching tanks for cobalt recovery. (Photo credit: Bioshale - BRGM) Stirred tank bioleaching - Bacterial oxidation of ground mineral slurry can be carried out in aerated agitated vessels, when the value of the metal is sufficient to justify the cost of installing and operating the equipment.

The reaction vessel can be either a mechanically stirred tank with a means of introducing oxygen into the slurry, or an air agitated Pachuca reactor where the introduction of the air provides not only the oxygen but the agitation of the slurry. The application of this process to ores has been fairly limited as the size of the vessels and thus the costs are often prohibitive.

The oxidation kinetics is much higher than in situ or heap systems. Concentrate systems require smaller tanks and therefore are less expensive but they do require a concentration circuit and generally more cooling.

Bio-oxidation Heaps - The heaps are formed in a similar manner to conventional heaps, by stacking crushed rock into constructed piles on prepared impervious pads that have a sloped base to allow solution to flow by gravity into collection drains. The difference is that as the rock passes off the end of the stacker, concentrate is sprayed onto it. Oxygen is added to the system to enhance the rate of oxidation by blowing low pressure air into the heap base. The heap is irrigated with low pH solution containing nutrients to promote bacterial growth.

For base metal sulphides the valuable metal is recovered in the solution; while for refractory gold treatment the bio-oxidized residue is removed for treatment by conventional processing. This system also allows ore to be treated simultaneously as the substrate can be oxidized at the same time. The advantages of this system are that it has a much lower capital and operating cost. The main disadvantages are the slower oxidation rates and difficulty operating in extremely cold environments.

CONSULTANTS

There are some 14 suppliers of mining-related biotechnology suppliers listed in the InfoMine Suppliers database and 14 consultants in the Consultants database (some are the same). One is BioteQ Environmental Technologies, which provides a comprehensive overview of their technologies. Applications include the Caribou Mine in New Brunswick, the Raglan Mine in Quebec and the Bisbee Mine in Arizona. As Time would have it all news is made by individuals not by some mysterious process. So here are potted biographies of the fellows who are making this happen:

  • Brad Marchant is a specialist in mineral processing and biohydrometallugy research, development and operations.
  • Richard Lawrence is a specialist in acid rock drainage, biohydrometallurgy, mining environmental management, and mine water treatment.
  • David Kratochvil is a chemical engineer, specializing in biotechnology and water treatment.
  • John York is a Chartered Accountant who served as Vice-President of finance for junior listed companies, including Zamora Gold and Battlefield Minerals Corp.

Maybe in time I will get to meet them and harness their knowledge for these pages.

Who could resist the name and the site Boojum Technology? Here are some successes they claim on their site for biotechnology:

  • The Chara Process named after the Characeae species of algae.
  • A substantial decrease in Ra concentrations was observed in effluent that passed through a bog which was populated with Nitella flexilis, an algal species of the Characeae.
  • The ARUM (Acid Reduction Using Microbiology) process has been field tested in a muskeg area to remove arsenic (36 mg/L) and nickel (79 mg/L) from waste rock seepage.

Lawrence Consulting Ltd describes their Biotechnology Services under these headings:

Process design and development for refractory gold and base metal ores and concentrates

  • Water treatment process design and development
  • Laboratory test program design and management
  • Participation in feasibility studies
  • Due diligence and feasibility studies
  • Troubleshooting plants, heaps and dumps

I went back a number of times to BioSigma, mainly because they have so extraordinary an introduction. Once on their site, I could get no information other than that they are a joint venture of Nippon Mining and Metals Company and Codelco-Chile. I did find a pdf that gives more information and lot of pictures on their technology.

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