Importance of Gold Recoverable by Gravity
The importance of gold recoverable by gravity concentration is important to design the gravity circuit and also to assess the final recovery of gold. This exercise comprises the selection of the recovery unit and feed preparation system (e.g. screen opening). It is not interesting to present to the gravimetric device a coarse particle, which has a low gold grade and lowers the capacity and efficiency of the recovery process due to some material is characterized by the presence of coarse and high density gangue, which tend to erode gold collected by the recovery unit, especially in the case of centrifugal concentrators. It is important to mention that prior screening is appropriate determine a size that may hinge on the coarsest particle that should be recovered.
When the particle size of the gold recoverable by gravity is fine and the main recovery process is flotation, it is important to consider a flash flotation circuit, which may decrease the circulating load of the gold recoverable by gravity below 200 mesh and the gravity circuit may follow the process. Most the time, low density gangue material is used to yield excellent gold recoveries by designing a simple recovery circuit. It has been noted that when the response of the test is intermediate to highly amenable, the information obtained must be reviewed carefully. it must be understood that since a gravity unit may recover gold with efficiency, the results at full scale plant will be lower than those obtained in the testing program. Essentially, the efficiency of the gravity circuit will indicate the level of variability and circuits with high efficiency can achieve a recovery equal to two thirds of the measured gold recoverable by gravity.
It has been noted in several gold projects that the economic incentives of gold recovery by gravity do not guarantee achieving the full gravity potential. There two factors that have influence, one is to include a gravity circuit in the primary and secondary grind circuits, which mean that non-liberated gold in the primary hydrocyclone overflow will not be recovered by a gravity unit. The second factor is related to the fact that gold recovery is influenced by the circulating load. In some gravimetric units a feed rate in excess will overload the equipment and a low gold recovery by gravity is the usual performance at full scale recovery plants with lower fraction of the circulating load processed by the recovery unit. Other treatment scheme is related to the installation of cyanidation to treat gravity tails. The economic justification of gravity recovery is considered following the basic principles of gold gravity. The performance of the cyanidation circuit is influenced by more factors than those considered in gravity circuits (e.g. mineralogy, locking, cyanicides, carbon, water quality). Also, if the gold recovery is improved by 0.5 or 1%, the payback period of the project is rapid.
Fluctuations in the daily performance of gold gravity circuit could be due to variations in mineralogical specimens rather than circuit performance. In this way, collecting and testing daily samples may easily confirm the source of the problem. For example, when a testing program evaluates the performance of different composites, the performance at the industrial operation is influenced by the ore type and the blending of the material fed to the plant.