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Process engineering company Appropriate Process Technologies (APT) has designed a simplified circuit for its low-energy processing plant that uses batch and continuous Knelson concentrators to capture elemental liberated gold, as well as sulphide carriers, reducing energy and space requirements. A number of process advantages were included in the design to improve the efficiency of the plant, with the emphasis on the reduction of energy use rather than solely on percentage recovery, says APT project coordinator Susan McMillan.
APT’s low energy process plants include an efficient impact mill. This is used rather than a ball mill. It crushes the ore and, although the general particle size is much coarser, the initial degree of gold and sulphide liberation is high, owing to the fractures formed on grain boundaries.
“This early liberation can account for most of the value contained in some ores, but a small secondary mill is included to further reduce the coarse and dense portion in the primary tailings,” she says. “The elemental gold is recovered gravimetrically directly to the gold bar. The sulphides, being coarser, can be extracted using simple vat leaching,” she adds.
The low energy process plants system operates at as little as 8 kWh/t as opposed to around 50 kWh/t used by a comparable conventional ball mill or carbon-in-pulp process.
“The small and compact system can be operated down a mine, with the tailings being pumped out rather than the ore being hoisted,” McMillan explains, “again reducing the energy used by the whole process.”
“Some ores are not suited to low-energy processing, but the system can supplement existing conventional processing by reducing the grinding energy, and also by recovering a portion of the gold before conventional processing,” she concludes.
APT designs low energy process plants that use early liberation techniques