LEACHING & SX / EW
concentrate with high levels of arsenic has exceeded treatment capacity in smelters. Today, only one smelter in the world is willing to treat large volumes of concentrates containing more than 1 % As.”
A high level of arsenic often correlates with a high gold grades, providing an additional source of revenue, but copper producers receive only partial credit from the smelter. For other metals such as zinc, lead, and manganese, they pay penalties to the smelters.
The ROL process covered at the beginning of this article can leach copper from arsenic-laden concentrates. By producing copper on-site, miners maintain control of and avoid having to transport arsenic-bearing residues. The ROL process furthermore enables recovery of pay metals on site and avoids the economic penalties imposed by smelters.
Another emergent technology, the Toowong Process, is now being commercialised after successful piloting. Toowong is a unique technology for the removal of As, Sb and other deleterious elements from base metal concentrates. The process selectively leaches the deleterious elements, leaving the metals of value in the concentrate as a premium clean product. The process uses alkaline leaching chemistry developed and patented by Core Resources in 2008-2012, and was demonstrated in a $ 4.5 million integrated continuous leaching pilot plant in 2012.
The pilot plant treated 1.5 t from three global resources: Bulgaria, Philippines, and Chile: n > 90 % As removal n Final concentrate > 0.1 % As, down from 1.1 % n Arsenic product generated n Low reagent consumption n Process demonstrated at continuous steady state. n Chemically separates arsenic at the mine site n Captures arsenic in an environmentally stable form n Returns arsenic to its original native location n Creates premium clean copper concentrate for shipment to smelter n No downstream copper metal recovery required n Environmentally superior technology n Enabling technology for stranded projects n Significant cost savings for current mines. The value that the Toowong Process presents for mining operations lies not simply in a treatment process for the removal of arsenic, but in its potential to enable a re-optimisation of the mining schedule without the constraint of planning around deleterious elements.
Recent work by Core, with its engineering partner, Mineral Technologies, and Whittle Consulting,
has focused on developing capital and operating costs for the Toowong Process, along with quantifying its potential overall impact on the NPV of an arsenic-constrained project. The ALTA Metallurgical paper, The Economics of Removing Arsenic from Copper Concentrates using the Toowong Process by Peter Rohner et al presents these results, as applied to an operation producing 40,000 t / y of copper concentrate.
Leach clarification
Effective clarification of silver and gold cyanide leach solutions, a key factor in the Merrill-Crowe process, is critical. Many silver and gold operations rely on Veolia’ s leaf filtration systems.
Veolia ' s Whittier™ filtration technologies help ensure a higher quality filtrate for better recovery in a reduced footprint. The Filtra-Matic™ pre-coat pressure leaf filter and Auto-Jet™ self-cleaning pressure filter are both ideal for leach clarification applications. Key benefits Include: n For tough filtration projects involving large flow rates n Particle removal down to 1 µ m n Durable leaves designed to provide maximum strength n Filter leaves designed for uniform flow distribution and cake formation n Auto Jet has improved cleaning with rotating leaves during spray sluicing n Quick opening door on Auto-Jet design n Hydraulic retracting shell or head on Filtra- Matic Thanks to a superior, patented sluicing design, Auto-Jet maintains its fully rated capacity even when heavy, sticky or unusually tenacious cake is encountered, Veolia says.“ Its efficient sluicing system ensures thorough cleaning of every square inch of filter surface area every time.”
Filtra-Matic is especially useful where a dry cake discharge is desired. Designed for operating efficiency and easy maintenance, this filter is offered in two basic models: the Filtra-Matic RT
with its unique retracting tank, and the Filtra- Matic RB featuring a retracting bundle design.
Watch your oxygen
As OreMax points out, oxygen is an essential element in the leaching process. Efficient heap leach operations require that oxygen plus the lixiviant be present to dissolve the mineral deposits into the leach solution. In general, the higher the oxygen level, the greater the mineral recovery. Applying too much leach solution saturates the crushed ore and drives out the oxygen. Maximum leaching efficiency is achieved when the leach solution moves through the ore by means of capillary action.
Ideally, solution percolates through the ore by
OreMax says“ the Max Emitter is the most plug resistant emitter available on the market today. Plugging results in reduced extraction and causes the system hydraulics to change thereby negatively changing the solution application rates. The patented emitter design enables lower flow rates without the dripper plugging. Using the Max-Emitter will usually increase extraction and bring mine performance much closer to original performance specifications”
means of capillary action leaving pockets of oxygen in the pores between particles. Applying too much solution hinders the leaching reaction. When solution has completely filled into the pores, the ore is said to be‘ saturated’. Bacteria, which are crucial to the copper leaching process, die from oxygen deprivation.
OreMax offers six suggestions to prevent leach pad saturation.
Use a tensiometer: Measure the moisture content of your leach pad at all times. This will give you the feedback you need to properly manage your solution application. It is recommended to use a tensiometer to measure each cell. This measures water potential or tension. Water potential is commonly measured in units of bars( and centibars in the English system of measurement) or kilopascals( in metric units).
Control your pressure: One of the major causes of over application of leach solution is not controlling the operating pressures of drip lines. A 15 % variance in pressure from the recommended operating pressure will cause a 15 % over or under application of solution. OreMax recommends using individual regulators to monitor pressure of
40 International Mining | NOVEMBER 2017