The operation of Reichert Cones concentrators at gold plants with crushing and comminution circuits has some operative problems that yield low gold recoveries. The explanation is not simple, but some plant metallurgists consider that thin steel flakes from broken grinding balls, nails from underground, bits of wire and other materials find their way through the slotted scalping screen ahead of the cone and enter the cone feed. Then, they are cemented onto the surface of the cone by pyrite with any degree of oxidation and possibly by carbonates that precipitate out of the water. Basically these surface conditions act as traps for free gold particles. It has been detected that up to 5 kilos of gold could be trapped in this manner and this is security risk.
The type of gravimetric circuit and configuration of the cone is other aspect to consider. For example in a 3 double single cone (3DS), the slots feeding the double cones could be blocked with wood and steel, rubble that prevent one of the double sections from operating. When this situation happens the solution is to modify the double cones to single cones. Other problem is related to the hatches, which could be very small for the deck surfaces to be inspected or cleaned properly. When larger hatches are cut, the feed distribution cone is distorted, leading to uneven feeding of the concentrating cones. The hatches generate loss of slurry as a result of splashing.
Operators have problems when the pulp density must be adjusted. It has been noted that many plants are not used to include a sampling point near the feed pumps and the operators try to estimate the addition of water to get the right pulp density. Also, the location of some pumps creates an unstable feeding flow to the equipment. Other problem is associated to the percent solids in the cleaning circuit. If there is no enough addition of water, the pulp density is high and consequently the feed is too dense for efficient operation.
Free gold particles are sometimes found in gold plant tailings and it reasonable to assume that the improvements in overall recovery when gravity concentration is employed as part of the recovery process are in part due to the recovery of these particles, which could be remnants of large gold particles or gold particles coated with iron oxide. Basically a cone concentrator performs better when the valuable constituent of the ore is liberated and has density sufficiently higher that of the gangue material for good separation to be possible. It is also essential for the feed to be correctly prepared by the removal of any rubble that could block concentrate ports and other opening of the concentration device. Other important factors are the feed rate and the pulp density of the gold ore being fed to the cone concentrator; these should be kept constant at the optimum values recommended as results of testing programs. When a gold gravimetric recovery process equipped with cones includes rougher and cleaning concentration stages, the control is critical.