National Aluminium Company Ltd (NALCO, India's largest domestic aluminium producer) has invited expressions of interest (EoI) for sourcing an environmentally friendly technology for a 10 tonne per annum (TPA) gallium extraction plant that it plans to establish at its Alumina Refinery in Damanjodi, Odisha State, India either through a joint venture or standalone. The firm targets gallium metal with a purity of >99.99% (4N+).
NALCO was incorporated in 1981 following investment by the Indian government in order to exploit part of the bauxite deposit discovered on the East Coast of India. The company was subsequently listed on the LME (London metal exchange).
NALCO operates a multi-location Bauxite Mines-Alumina-Aluminium complex (along with a captive power plant) in Odisha. A major expansion program (Phase 1) was completed in 2001, and a Phase 2 expansion was completed in July 2012, leading to an upgrade of the firm's refinery activities and ongoing upgrade of its mines. The firm has bauxite mines in the Panchpatmali hills of Koraput district in Odisha, with a capacity of 4.8 million tonne per annum (MTPA) that is being expanded to 6.3 MTPA.
"NALCO invites EOI from the interested and competent manufacturers/technology suppliers interested in providing technology for extraction of gallium from Nalco Bayer liquor (intermediate process liquor generated from digestion of bauxite by the Bayer process) and having expertise in production and marketing of metallic gallium or gallium compound," the firm says.
The process of extracting alumina from its mineral bauxite in caustic liquor solution is known as the 'Bayer' process. Bauxite received from the mines is either stacked in stockpile or fed directly to a secondary crusher for size reduction. Secondary crushed bauxite from the silo is fed to the ball mill, along with caustic liquor for grinding. Ground bauxite slurry after pre-desilication is digested at atmospheric pressure (at a temperature of 105-106°C) for the extraction of alumina. Undigested bauxite is separated as red mud. Aluminate liquor is cooled to precipitate ATH (alumina trihydrate), which is calcined to produce alumina. Gallium dissolves in the liquid phase and becomes enriched over time as NALCO has not been extracting gallium metal or any compound until now. However, some gallium escapes from the plant liquor during the discharge of red mud as well as with product alumina.
