Mineral Oxide Bioleaching Using Fungal Metabolic Products
A process that achieves high value metal (Ni, Co, V, Ti) extraction from oxide ores at temperatures of 90-95°C within 3 - 6 hours.
Three hydrometallurgical process routes are used commercially in processing Ni laterite ores; high pressure sulphuric acid leaching (HPAL), atmospheric acid leaching (AL) and heap leaching. The strength and weaknesses of these processes has been a subject of debate for many years.
In general the three key features that allow the process to be competitive are CAPEX, nickel recovery, acid consumption and minimal dissolved impurities (in particular iron) in the leaching solution. HPAL is achieved at high temperatures (between 250 - 270 °C) and high pressures.
While the metal recoveries are high (~95-99% Ni), the CAPEX and energy usage in this process are also high. Atmospheric acid leaching is achieved at temperatures between 90 °C and the boiling point of the solution. The key issues for AL are its kinetics of leaching and the generation of significant concentrations (~60% extraction) of iron and aluminium and lower nickel and cobalt extractions compared to HPAL.
To achieve high nickel extraction (~80-90%) requires 800-1000 kg/t of dry ore of acid and leaching periods from 10-18 hours in a single stage leaching process.
Highly serpentinised ore (MgO>30%) allows shorted leaching periods, however the acid usage is usually higher because of the greater neutralising capacity of the mineral.
Our process is an improvement to the atmospheric acid leaching process by achieving higher metal recovery, greater selectivity and faster leaching from a broader range of highly stable oxide minerals including nickel laterite ores (from limonite to the more difficult to leach high-iron transition zone saprolite feed), ilmenite (primary and weathered) and magnetite spinels.
The process involves leaching with a combination of selected organic acid(s) and sulphuric acid at temperatures from 85°C to the boiling point of the leaching solution to extract 90-99% of the value metals (Ni, Co, Ti and V) with reactions times of 3 to 6 hours under atmospheric conditions.
High metal recoveries and rapid leaching is achieved as a result of a combination of processes including reduction, complexation and acidification of the host minerals. Selective leaching is achieved.
The Fe: Ni (kg/kg) ratio in the final leaching solution is typically about 1.7-4.4 for saprolite and 8.0-12.0 for limonite. The amount of sulphuric acid used in a 30% pulp density single stage leaching of saprolite ore is about 426 kg/t of ore (25 kg/kg Ni) and the organic acid consumption is 16 kg/t of ore (1.75 kg/kg Ni).
Further reduction in acid consumption is achieved in a continuous counter current system.
Bioleaching metal values including nickel, cobalt, titanium and vanadium from oxide minerals of nickel laterite, primary and weathered ilmenite ores and titaniferous magnetite concentrates.