Impurities such as magnesium and zinc, it says. A cesl plant can be located

on-site. Current work on the company’s nickel processing technology focuses

on the production of separate nickel and cobalt intermediate products

using a novel solvent extraction process. Flowsheet enhancement work is

underway to evaluate different processing methods for producing nickel

metal from various intermediates.Simplicity

The many innovations that appeared during the past few years range from

complex flowsheet development to simple, yet ingenious improvements,

often resulting in lower energy requirements and cleaner operation. An example is a simple, yet novel approach to pressure oxidation leaching

called the Activox process, marketed by Norilsk Nickel (Moscow, Russia;

www.nornik.ru). The process is a combination of fine grinding and pressure

oxidation, resulting in milder operating conditions. Conventional pressure oxidation operates at temperatures exceeding 200°C with overpressures of 2,200 kPa or more. Activox is a form of pressure oxidation

that operates at temperatures of about 100°C and pressures of 1,000 kPa. The milder operating conditions simplify the engineering requirements

and reduce costs, yet maintain the advantages of pressure oxidation,

says the company. The process breaks down sulfide

minerals by reacting them with oxygen to produce discharge slurry consisting

of a solid residue and liquor. The company has developed downstream

flowsheets for concentrates containing nickel, cobalt and copper,

using well established solvent extraction technology.

The Activox process has been demonstrated in several pilot plants.

The latest pilot plant was the Tati nickel plant in Botswana, in southern

Africa.

Fine grinding is also at the basis of the Albion process, developed by MIM

Holdings, now Xstrata Plc. (London, U.K.; www.xstratatech.com).

The process, intended to treat concentrates produced from refractory

base and precious metal ores, consists of a hot oxidative leach of finely ground

concentrates at atmospheric pressure. The company says the development

of the process paralleled the development of new fine grinding mills. This

has enabled leaching to be carried out under far less demanding conditions

than previously required in pressure or bacterial leach plants.

The process was recently commissioned at Xstrata Zinc’s Nordenham

zinc demonstration plant in Germany, which commenced operation in

January this year. Designed to treat 40,000 ton/yr of concentrate, it has

been able to treat up to 56,000 ton/ yr of concentrate. The company said

it is conducting a feasibility study to expand its Albion plant to produce

150,000 ton/yr of concentrate, with a view to commissioning the expansion

in late 2013. The company has also been operating

a demonstration plant for the Albion process at the San Juan de Neiva

zinc refinery in Spain, which started up in July of last year. It is designed

to treat 9,000 ton/yr of concentrate to produce 4,000 ton/yr of metal. Xstrata

Zinc is studying the option of treating 220,000 ton/yr of concentrate in

an expanded Albion plant, to produce 100,000 ton/yr of zinc metal, with the

intention of reducing operating costs and energy consumption. The expansion is planned to be commissioned in early 2014.

Both plants treat zinc/lead bulk concentrate from the McArthur River

Mine in Australia. The concentrate is ground in a bank of M3000 IsaMills at

the mine prior to transport. A third Albion plant — for gold production

— is scheduled to be commissioned in December this year at the

Las Lagunas tailings-treatment project in the Dominican Republic. The

plant is designed to produce 65,000 oz/yr of gold and 600,000 oz/yr of silver.

An M3000 IsaMill is installed on site.

Tackling the hard stuff Since the “easy stuff” has already

been found and processed, the industry has been increasingly turning to

the not-so-easy stuff, including nickel laterite ores. These have been the

main target of Direct Nickel Pty Ltd (Sydney, Australia; www.directnickel.

com). The company’s hydrometallurgical process to treat nickel laterite

ores will be tested at CSIRO’s minerals processing facility at Waterford in

Perth. It involves tank leaching at atmospheric

pressure and moderate temperature. The process uses nitric acid,

instead of the sulfuric acid commonly employed for treating nickel laterite

ores. The nitric acid is continuously recycled. Nitric acid consumption

is about 30 kg/m.t. of feed material, versus 300–1,000 kg/m.t. for sulfuric

acid-based leaching. Extraction efficiencies are about 95% of nickel and

85% of cobalt. Direct Nickel says alternative processes

are uneconomic when the magnesium content of the ore reaches 3%,

whereas there is no upper limit for the its process. It says operating and capital

costs are about half those of existing processes.

Biohydrometallurgy While all the technologies described above involve chemical and mechanical processes, a new field — biohydrometallurgy,

including bioleaching — has opened up, involving the use of

bacteria and other microorganisms to do part of the job.

For example, technologies for bioleaching sulfide ores in an engineering heap environment have been developed by GeoBiotics LLC (Lakewood,

Colo.; www.geobiotics.com). The company’s two main technologies are

Geocat and Geoleach. The company says Geocoat combines

the low capital and operating costs of heap leaching with the high recoveries

associated with other processes, such as roasting, pressure leaching, or

stirred-tank biooxidation. The process is applicable to refractory sulfide gold

concentrates and to sulfidic copper, nickel, cobalt, zinc, and polymetallic

base metal concentrates. The Geoleach process uses iron- and sulfur-oxidizing microorganisms to facilitate the oxidation and leaching of sulfide minerals. The organisms include mesophile bacteria (Thiobacillus

ferrooxidans, Thiobacillus thiooxidans, and Leptospirillum ferrooxidans)

and moderate and high temperature thermophillic bacteria, such as the Archaea

Sulfolobus and Acidianus. The outlook The present challenges faced by the

minerals processing industry have stimulated the development of much

good technology and science. Many companies and organizations around

the world are doing research on issues including the following:

• Using microorganisms to develop a heap bioleaching process for treating

low-grade chalcopyrite ores

• Controlling ferrihydrite precipitation