Part of key information to calculate the gravity recoverable gold is taken from the grinding circuit, and especially of the hydrocyclones performance. The unique behavior of gravity recoverable gold in hydrocyclones explains most of the high gold circulating loads observed, slow grinding kinetics is also a contributing factor. The grind product also affects the grinding kinetics of the gravity recoverable gold and how much fine gold will be liberated. Both effects have an impact on gold gravity recovery, but not as much as the partition curve. The amount of gravity recoverable gold at each pass is in fact a key variable affecting how much gold will be recovered by gravity, and defines what is considered as gravity recovery effort. Basically, the gold gravity recovery effort correlates with how much gravity recoverable gold is recovered, and next to the amount and size distribution of gravity recoverable gold, is the most important factor affecting gold gravity recovery.
Maximizing gravity recovery should not be the main objective of the gravity circuit, as the downstream circuit would recover most of the gold not recovered by gravity. The optimum gravity recovery is dictated by its economic incentive. There is an interaction between the nature of gravity recoverable gold, the recovery effort and the economic incentive of gravity recovery. The calculation procedure involves a link between the recovery effort, the size distribution of gravity recoverable gold and the fineness of grind by a simple multi-linear regression. In the metallurgical lab is important to generate a large data set of simulations using different sizes distributions of gravity recoverable gold and a variety of dimensionless grinding times, partition curves and recovery effort. The database is analyzed using multi-linear regressions. Two regressions are produced, one for fine gold recovery and other for coarse gold recovery.
There is a linear link between gravity recoverable gold and the recovery effort; rather, gravity recoverable gold is usually proportional to the logarithm of the recovery effort, which implies that there is a rapidly diminishing return to increasing the recovery effort. Use of an incorrect recovery effort either results in a failure to tap fully the economic benefit of gravity recovery, or the bloated capital cost of an oversized circuit.
As long as the gravity recoverable gold is determined accurately, the recovery effort is properly estimated and a reasonable estimate of the partition curve of gravity recoverable gold is available. The gravity recoverable gold test when performed on a representative sample provides the necessary information about the ore, leaving a proper estimation of the recovery effort and the partition curve of gravity recoverable gold. A databank should be prepared in order to get information of the gravity recoverable gold as a function of operating conditions for various gravity recovery units. The unit most used for gold recovery by gravity, centrifugal concentrator, is used to perform the basic tests and the information obtained must be updated as equipments evolve their design (e.g. bowl design, speed).
For design purposes overall gravity gold recoveries or recovery effort and regression may be used to predict recovery. For optimizing purposes, it is much preferable to measure the size-by-size gravity recoverable gold of the existing gravity units and the recoverable gold according to the partition curve. This information can be used in a more accurate size-by-size gravity recoverable gold model. Care should be taken when using an overall recovery effort due to gravity recoverable gold is extremely size dependent and overall recovery is strongly dependent on the size distribution of gold in the feed.