Biomining

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Step 1: Mining of the mineral sulfide ore  Step 2: Flotation to form a mineral concentrate  Step 3: Bioleaching and/or biooxidation to release the metals  Step 4: Metal recovery to produce a valuable resource
Step 1: Mining of the mineral sulfide ore
Step 2: Flotation to form a mineral concentrate
Step 3: Bioleaching and/or biooxidation to release the metals
Step 4: Metal recovery to produce a valuable resource

Biomining is applied bioleaching and biooxidation with the aim of extracting metals from ore in contrast to acid mine drainage which is uncontrolled and unintentional.

Questions

  • When is biomining economically viable?
  • What advantages does biomining have over other metal extraction methods?
  • Disadvantages?

Difficult to answer these questions generally. Every situation has new Techno-Economic factors. The choice of technology is usually an iterative process with a lot of tests.

The Biomin BIOX® Technology For The Treatment Of Refractory Gold Concentrates

In 2016 Biomin will celebrate 30 years of successful operation of their BIOX® Technology in 12 commercial plants commissioned in nine countries worldwide treating pyrite / arsenopyrite gold concentrates.

From the Fairview plant commissioned in 1986 in South Aftrica to the latest plant to be commissioned in the Philippines during 2015, it was nothing else but a huge success story. During this period the treatment capacity of the operating plants were increased form a mere 10 tons / day concentrate to more than 2000 tons / day concentrate at the Kokpatas plant in Uzbekistan. Reactor sizes were increased from 60 m3 to 1600 m3. Pyrite / arsenopyrite concentrates containing up to 34 % Pyritic sulphur and 24 % arsenic can be successfully treated.

The BIOX® Technology was originally developed by Gencor in the late 1970’s and commercialised through its wholly owned subsidiary Biomin Technologies S.A. With the merger of Gencor and Golfields SA 1998 Biomin became a subsidiary of Gold Fields Ltd. Since 2013 Biomin Technologies S.A. is wholly-owned subsidiary of Biomin South Africa (Pty) Limited – the company established through management buy-out of the BIOX® Department of Gold Fields Ltd.

Since the commissioning of the first commercial plant in 1986 at the Fairview the efficiency of the process was continuously improved through ongoing research and development work conducted on laboratory scale, and tested and confirmed at Fairview. These improvements included increasing the solids content of the concentrates in the reactors from 10 % to 20 %, increasing operating temperatures from 35 0C to 45 0C, reducing overall residence times from six days to four days and improving agitation and aeration efficiencies in the reactors to increase oxygen utilisation from 25 % to 40 %.

The BIOX® Technology is wholly owned by Biomin South Africa and marketed worldwide providing the technology to clients on payment of a negotiated license fee. Biomin also provides the following detailed services to assist potential clients with the evaluation of their refractory gold ore bodies and the amenability of their concentrates to the BIOX® process. These services will include laboratory amenability tests, initial scoping studies to confirm viability of the process and the project, full scale pilot plant tests, capital and operating costs, for pre-feasibility studies and process design criteria for the feasibility and bankable studies. Assistance with the inoculums build up and plant commissioning will also be provided. Ongoing support services to confirm efficiency of operations can also be contracted.

Over the 30 years of operation the BIOX® Technology has been confirmed as the first choice Technology for treating of refractory gold concentrates yielding excellent final gold recoveries and being environmentally friendly with residues deposited with stable arsenic precipitates. Continuous sampling of tailings dams at Fairview and the Wiluna Mines in Australia have confirmed that the arsenic precipitates are indeed stable. The technology has been proven to operate under all climatic conditions from high humid temperatures in Ghana and desert conditions in Australia to cold winter conditions in Kazakhstan and Uzbekistan.

Where does the technology go from here? At the MEI Biohydromet conference held in Falmouth in 2014, it was very encouraging to see the number of Research Institutions and Universities now doing work on bio-oxidation and bio-leaching. Unfortunately, however, from all the papers presented by the Institutions and students, there were no exciting developments reported. Researchers have really only confirmed the process which was developed in the 1970’s and commissioned on commercial scale in 1986. Students for example, reported that concentrates can be successfully treated by bio-oxidation to remove arsenic. All the work reported was done with 1 % solids in pulp. This confirms nothing as BIOX® operations were already treating 20 % solids in 1968 and removing arsenic in the order of 8 %.

Researchers should really concentrate on the further development of the process considering treating of higher % solids ( 30 % - 35 % ) for mesophiles and specifically concentrate on generating thermophile strains that can operate at solids content much higher than the current confirmed 10 % when treating copper concentrates and 17 % for nickel concentrates . Further potential improvements could be to improve reaction kinetics to reduce residence times in the reactors to under four days for gold concentrates and seven days for copper / nickel concentrates.


Pieter van Aswegen

(Formerly Senior Manager Metallurgy at Gencor and Gold Fields before retiring in 2006)

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