More mineral processing news
So many new ideas were floated at the CMP meeting that it is impossible to describe them all in our pages. But for readers with interests other than grinding, here are a few highlights of other technologies that were discussed.
-As bubble surface area flux looks to become the standard for characterizing gas dispersion in flotation cells, sensors are needed to detect the two major variables–gas hold-up and gas velocity. A new device to measure the latter has been created by the thinkers at McGill University and Noranda. A vertical, clear plastic tube is suspended in the pulp zone. It is closed at the top, and a pressure transmitter detects increases (measured as cm/sec) as bubbles rise and burst in the tube. The instrument shows promise as a method of circuit optimization at the Brunswick mill. It detected faulty air valves and gas flow meters, and was useful in determining the effective working range of the manual air control valves.
-Noranda and Heath & Sherwood have developed a new on-line method of measuring concentrate moisture levels. The mechanical parts are simple: a drag force transducer behind a v-shaped plow. The plow controls the thickness of the concentrate on a moving belt. In both the Horne and Brunswick concentrators, this equipment has provided a cheap and timely method of controlling dewatering processes and reducing costs.
-Outokumpu has two new mechanisms to improve flotation performance. The FrothMaster aims to control the speed at which froth is recovered over the lip of a flotation cell, thus improving grade and recovery. This relatively inexpensive, vision-based system has been successfully installed in rougher cells at the Cadia Hills gold mine in Australia. Results include successful balance of concentrate mass-recovery between two cells in series on the same level; control of froth speed within 5% of its setpoint; control of first rougher concentrate grade within 0.3% of grade setpoint; and reduced frother consumption.
-The FrothBuster, also from Outokumpu, removes entrained air from concentrate slurry before the bubbles add to operating problems in thickeners. Such deaerators have been installed on the thickener bridge at Normandy Mining’s Golden Grove base metal operation. Within eight hours of start-up, the mechanism had dispersed residual froth and there were no signs of rebuilding.
-A rotating biological contactor, familiar to the municipal wastewater treatment industry, looks like a disc filter. Micro-organisms grow on the discs and are submerged periodically in the wastewater as the discs rotate. Biological activity removes toxins. Sounds simple enough, but do they have an application in mineral processing? Yes, according to research conducted at Canmet. The project focussed on the removal of ammonia by converting it to nitrate. The contactor removed more than 95% of the NH4-N in simulated mine effluent at a pH of 7-8 and a retention time of 72 minutes. Ammonia in the effluent was lower than 2.0 mg/L. The advantages of such systems include low energy consumption, easy operation and low maintenance needs.
-The toxic nature of cyanide is fuelling research into alternatives for gold recovery. Joint research done at Queen’s University, Canmet and CSIRO (in Australia) has investigated thiosulphate leaching as an option. So far the results are not promising. Using thiosulphate is more costly than cyanidation, and there are several problems that came to light. Gold recovery from thiosulphate solution is difficult. The reagents create ammonia and reagent consumption is high. Mild steel equipment suffers corrosion. More work on thiosulphate leaching is needed to make it an economic alternative.
The Proceedings of the 33rd Annual Meeting of the Canadian Mineral Processors may be ordered from Angela Putz, CMP Secretary, 580 Booth Street, 12th Floor C6, Ottawa, Ont., K1A 0E4; phone 613-943-9217; fax 316-943-9215; e-mail [email protected]