Sometimes, many designers try to avoid the basic stages to design a gold gravity recovery circuits and the consequences of these bad practices are significant in the metallurgical performance and profitability of the project. The testing program may have a number of applications, some of which can generate different diagnostics or outcomes. If the material shows a poor response in the gravity test, the gravity option should be excluded in the design. Basically, it is important that the testing program and the gravity concentration test be capable of showing the weak and strong qualities of the material because the performance may be very erratic. When a gold gravity concentration circuit has been designed in before the ore was tested, the poor response of the test was indeed correlated with an even poorer plant performance. In this circumstance, the quantity of liberated gold may be good, but the presence of locking particles or other heavy minerals such as pyrite and the presence light gold and silver bearing minerals tend to affect the global performance.
Other impact of bad practices is related to the economy of the project. It means that the economical evaluation of the results is important. There several gold-copper operations around the world whose design included a gold gravity circuit to recover most of the free gold into the copper concentrate by installing a flotation cell. In this case the copper concentrate has an important benefit, which must be carefully studied. The most sensitive case is related to polymetallic deposits with significant silver and gold contents. For examples, if the gold is not recovered in the right point, it would be reported to the zinc concentrate and the economic benefit of the project is affected. For this reason the testing program must cover all the possible options, which may difficult to achieve high gold recoveries.
Gravity separation has the potential of providing an economical means of recovering and concentrating many types of gold ores. Laboratory separations and small scale testwork can provide data for reliable design of treatment plants. Sometimes, as little as 2-3% of the gold in the circulating load is recovered at each pass and overall gold recoveries of 20 to 50%, or one two thirds of the gravity recoverable gold, are usually obtained. Contrast this with most mineral circuits in which feed is exposed to rougher-scavenger recovery only once, and recoveries near 100% of the recoverable species of value at acceptable concentrate grade are the objective of the recovery process. Other important differences are the very high upgrading ratios, low weight of concentrate, and much smaller size and capacities of the cleaning circuits when compared to the roughing stage. The basics steps required to get a first design of the gravity circuits comprise the evaluation of the need for gravity, the gravimetric characteristics of the material, estimation of the gold recovery and selection of the optimum recovery effort to obtain an acceptable operation. Essentially, increased overall recovery may not be the only economic factor when considering gravity recovery. Additional factors include decreased costs for the downstream circuit, both capital and operating, reduced gold inventory, and increased security. The latter is a significant factor in the renewed interest in gravity recovery in many places in South Africa. Many Australian plants use coarse grinding and very short retention times in cyanidation circuits, both factors contributing significantly to the economic impact of gravity recovery