For a long time has been recognized that when the ore body present important quantities of coarse gold, exists advantages in recovering this free gold in the grinding circuit so that can be reduced the risk of coarse free gold being locked up in the primary grind. Also, reduce the inventory of activated carbon to be handled and minimize the potential risk of gold passing out of the cyanidation circuit only partially leached. Without any doubt, free gold particles can be recovered and concentrated by several gravimetric devices that utilize the significant difference between the specific gravity of gold and waste materials. Gold-bearing minerals and grinding media are in contact and form fine particles and chips of steel, which behave in a similar manner to the gold in the concentration process. Essentially, all these materials have to be removed to generate a concentrate suitable for direct smelting and several stages of cleaning is usually required. Obviously, other aspects such the form of gold particles has an impact on the recovery process.
The cleaning stages inevitably involve some losses of gold from the final concentrate. The non-concentrated material containing important quantities of gold are returned to the primary grind or regrinding section for liberation. Then, the opportunity for high gold recovery is lost. Although, the presence of gold in the recycle streams is variable, and some surveys of the gravity concentration process, indicate that it can be 30-50%. Considering this problem and with the idea of improving the gold recovery from the early gold concentrate, some metallurgists suggest performing the cyanidation of this material and the type of equipment is variable. The agitation method is the most critical aspect. Probably, the most common system of agitation is a high speed propeller mixer and the least expensive solution recovery system, settling and decanting. Once the pregnant solution is obtained and considered the gold content, it can be sent to the main cyanidation circuit or to the electrowinning process for direct recovery of gold.
One of the most successful equipments to recover free gold is the Knelson concentrator and the manufacturer offers a very important solution to recover and minimize the losses of free gold by the intensive cyanidation of the gravimetric concentrate in a reactor called Acacia. Many gold operations have something in common; the recovery of gold is high into the Knelson concentrate, but the subsequent concentration stages in other devices such as a shaking table results in significant gold being recycled to a previous stage. The intensive cyanidation of the gravimetric concentrate is attractive and optimizes the metallurgical performance of the operation.
Gold particles formed during primary grind Knelson Concentrators