A NEW COMMERCIAL METAL RECOVERY TECHNOLOGY
UTILISING ON-SITE BIOLOGICAL H2S PRODUCTION
Juan A. Pérez and Sergio González
Company NN, Chile
Rick Lawrence and David Kratochvil
BioteQ Environmental Technologies, Canada
John M. Smith
Company XYZ, USA
ABSTRACT
Phelps Dodge Mining Company and BioteQ Environmental Technologies Inc. have, through
their joint venture company Copreco LLC, constructed and are operating a new plant for the
recovery of copper from low grade leach solutions at the Copper Queen Mine in Bisbee,
Arizona. The plant utilises BioteQ’s BioSulphide® process technology, which uses a high rate
anaerobic biotechnology for on-site production of H2S from elemental sulfur. At Bisbee, the
biogenic sulfide reagent produced is used to precipitate copper into a high-grade copper sulfide
concentrate from the pregnant leach solution draining from a low grade stockpile. The Bisbee
plant is one of three commercial plants utilising BioteQ’s technology for metal recovery and/or
to produce high quality water for environmental discharge. A fourth plant is under construction.
Sulfide demands in the four plants range from 50 kg/day to 3.7 tonnes/day. Details of the Bisbee
copper recovery operation are presented, together with a discussion of the main advantages of
applying the biogenic H2S production in mining and metallurgical processes. Environmental
and economic benefits are demonstrated using data from existing operations.
INTRODUCTION
Recovery of copper, nickel, cobalt, zinc and other metals from leach solutions in
hydrometallurgical processes can be carried out by a number of proven technologies, notably
direct electrowinning, solvent extraction–electrowinning, cementation with iron (for copper),
and sulphide precipitation. The selection of one method over another depends on a number of
factors, including the solution chemistry, the pregnant leach solution (PLS) flow rate and grade,
the form of the metal product, the availability and cost of consumables, and the capital cost. In
general, high metal mass flows (solution flow and grade) are necessary to justify the capital
expenditures of solvent extraction and electrowinning technologies. Furthermore, the
metallurgical efficiency and cost effectiveness of these processes can be reduced as feed metal
concentrations decline [1, 2].
The BioSulphide® Process [3, 4, 5], which produces low cost H2S for use in selective metal
precipitation, offers a low capital cost alternative which can operate efficiently and costeffectively within a wide range of flows and solution grades. Since the technology can be used
to recover metals from solutions with low flows and metal grades [4], the technology is also
applicable to environmental applications for water treatment, with the sale of recovered metals
providing an offset to treatment costs [4]. For environmental control, the technology has a
distinct advantage in being able to meet strict effluent discharge criteria due to the very low
solubility of metal sulphides. For all applications, the on-site and on-demand generation of the
sulphide reagent means that the disadvantages of transport, storage and handling, associated
with the use of chemical sulphide reagents for metal winning, are eliminated [4].
Biological Production of Hydrogen Sulphide
A simple schematic illustrating the production of hydrogen sulphide in the BioSulphide®
Process is provided in Figure 1.
Figure 1: Biological generation of hydrogen sulphide gas
Hydrogen sulphide is produced by reacting ground elemental sulphur with an electron donor,
such as acetic acid, in the presence of sulphur-reducing bacteria under anaerobic conditions
according to Reaction 1.
4S + CH3COOH + 2H2O → 4H2S + 2CO2
(1)
The sulphur reducing bacteria act as a catalyst enabling reaction (1) to proceed kinetically
forward at 25°C and the system pressure of + 30 cm WC. A continuous production of H2S is
achieved by removing the gaseous products of the Reaction 1 from the bioreactor. Since
elemental sulphur is used as the sulphur source for making H2S, instead of sulphate, no process
water other than that contained in the reagents required for Reaction 1 enters the bioreactor.
Thus the bioreactor is a true stand-alone H2S generator.
The main advantages of using the biological H2S generation include:

Low cost of sulphide compared to the cost of Na2S, NaHS, or H2S Minimal hazards and
increased safety mainly due to the low system pressure and low inventory of H2S. At any
point in time the amount of H2S stored in the bioreactor(s) is a small fraction of the daily
H2S production. This often allows the avoidance of special environmental permitting of
reagent storage.
- Low capital cost mainly due to the ambient temperature and pressure in bioreactors that
are designed as conventional stirred tanks compared to pressure vessels with expensive
agitator seals.
-
Easy to scale-up and down over a wide range of H2S production capacities.
The model equation representing the kinetic process is summarised as:
2 b kr
 =  [CA0]n t
B 0
(2)
Copper Recovery at Copper Queen Branch, Bisbee, Arizona
Following evaluation of several mine sites in the south western United States, the Copper Queen
mine site in Bisbee, Arizona, was selected to construct a BioSulphide® plant for copper
recovery from the acidic drainage of the large #7 low-grade stockpile. The stockpile had been
under leach for some years, with copper recovered from the PLS in an iron cementation
precipitation plant, although decreasing copper grades and higher operating costs relative to
copper price led to closure of the copper winning circuit in 1999.
Engineering, construction and commissioning of the new BioSulphide® plant took place in
2003 -2004. The plant was designed to treat 40 m3/h of pregnant leach solution (PLS) with the
following typical composition:
Table 1: Bisbee PLS composition (typical)
Copper
340 mg/L
Total iron
1,800 – 2,500 mg/L
Ferric iron
Zinc
700 mg/L
930 mg/L
Manganese
1,620 mg/L
Aluminum
3,950 mg/L
Magnesium
2,890 mg/L
Calcium
pH
500 mg/L*
2.2 - 2.4
*Note: This is the note to the table
The BioSulphide® plant
Plant is located at the north east corner of the stockpile adjacent to a holding tank where PLS
from two solution collection dams is pumped. The pump station which returns solution back to
the top of the stockpile for distribution is also located in this area.
Copper is precipitated as CuS without pH adjustment, and without a significant amount of
precipitation of other heavy metals present in the water, to produce a product with
approximately 40% Cu. The contactor off-gas is recycled to the bioreactor where it is used to
strip H2S from the bioreactor liquor to the gas phase. There is no gaseous discharge during
normal operation. H2S and CO2 are consumed by the process and N2 is recycled as a carrier gas.
The plant is equipped with a caustic gas scrubber to capture any gas bleed, which might occur
on an infrequent basis, with the resulting NaHS added to the contactor.
Figure 2: Water flows involved in an ore/waste dump
The plant controls
The flow and grade of PLS fluctuate year round depending on the water management around the
stockpile and precipitation events. The plant controls adjust to the changes in the feed
composition automatically. In general, copper and ferric iron grades have been significantly
above design. In the case of copper, higher grades has allowed good daily metal production to
be maintained even though PLS availability to the plant has been below design due to drought
conditions in recent years. Higher ferric iron concentrations has, however, resulted in higher
than design sulphide reagent consumption and lower relative copper grades in the concentrate
product due to dilution by higher levels of elemental sulphur. Overall performance of the
bioreactor has, however, exceeded design capacity with respect to the amount of hydrogen
sulphide produced per unit volume.
CONCLUSIONS
The BioSulphide® Process has been successfully commercialised at the Copper Mine in
Arizona. The plant recovers copper as a sulphide concentrate from the drainage of a low-grade
stockpile. The commercial plants have demonstrated that the process permits a profitable
recovery of metals such as copper, nickel and cobalt from low grade solutions that cannot be
processed economically by conventional technologies such as SX-EW. Plants have relatively
low capital cost, allowing fast capital pay-back and profitable metal recovery in projects with
relatively short duration and/or with lower grade solutions. The operating results from the
existing plants show that the process can be operated safely, integrated with existing
conventional treatment plants, and produce treated water quality that can be discharged directly
to the environment [6].
In summary, the niche markets for the BioSulphide® Process have been identified and include:

Metal production (Cu, Ni, Co) from low grade solutions either as a stand-alone plant or
integrated with a conventional lime treatment plant.

Wastewater treatment to meet stringent metal discharge environmental standards with
concurrent toxic waste sludge volume reduction or elimination.
Supply of low cost H2S as a reagent to mineral processing and hydrometallurgical processes.
NOMENCLATURE
a
d
m
A
C
D
E
F
T
V

activity, %p/p
average particle size, m
mass, kg
surface area, m2
concentration, g/L
diffusion coefficient, m2/s
redox potential, mV
Faraday´s constant, 96487 coulomb/mol
temperature, ºC
volume, m3
stoichiometric coefficient
REFERENCES
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Gupta, C. K. & Mukherjee, T. K. (1990) Hydrometallurgy in Extraction Processes. CRC Press, Boca
Raton, Florida, U.S.A., pp. 33-35. [2]
Karamanev, D. G., Nikolov, L. N. & Mamatarkova, V. (2002) Rapid Simultaneous Quantitative
Determination of Ferric and Ferrous Ions in Drainage Waters and Similar Solutions. Minerals
Engineering, vol. 15(5), pp. 341-346. [3]
Kratochvil, D., Lawrence, R. W. & Marchant, P. B. (2005) Applications of Biological H2S Production
from Elemental Sulfur in Mining and Hydrometallurgy. ALTA 2005 Conference, Nickel/Cobalt &
Copper, Perth, Australia, May 16-20. [4]
Rowley, M. V., Warkentin, D. D. & Piroschco, B. M. (1996) Process for Treating Solutions Containing
Sulphate and Metal Ions. US Patent 5,587,079. [5]
Neville, D. (2005) The Future is GE Free, Los Angeles Times. Retrieved 28 September 2005 from
http://www.greenpeace.org.au [6]