Absorption of Activated Carbon

The active carbons used for such an effect are of a granular structure, being more apt the fabricates starting from the crustiness of coconut due to its hardness, which make it more resistant to the rupture and abrasion, and because it has proven, besides, that its absorbant capacity is generally higher than that of activated carbons (12). The most common pelletmetries of the commercial activated carbons of tis type are – 6/ + 16 – 8 + 18 and – 10/ + 20 wire metting. Some new carbons of herdness comparable are those fabricated by extrusion, as the NORIT (&), whose pellets of cylindric form confer to it more resistence to the mechanical attrition. These carbons, even though they are specially prepared for the carbon-in-pulp process, they have also found application for treating solutions of cyanidation in heap leaching.

The amount of gold and silver which a determined active carbon can carry depends, between two factors, of the concentration of these elements, the cyanide free of impurities, and the pH of the solution, besides the flux of the alimentation. Its pelletmetry also influences it, due to the fact that the fine particles, with its highest specific surface, can quickly get larger quantities than the thick ones, even though they must possess a minimal size to avoid losses by dragging in the efluents. One carrying of 12 kg. of precious metals per ton of carbon is a considerable price which is desireable for the industry, but if the concentration in the alimentation is too low, for example 1.5 mgpl of Au, it will difficultly reach to more than 6 kg. Au/TM in the carbon (12). In the diverse operations of the State of Nevada, where the minerals are processed at a very low law, the normal laws reached by the carbon vary between 3,5 and5 kg. Au/TM.

In a typical operation of adsorption, the solution which proceeds from the heap leaching is made to go through 4 or 5 columns in series, each one of these containing the same amount of carbon. The first column which is contacted with the solution is removed periodically from the circuit once that the carbon has been loaded, placing it later in the last place with fresh while the remaining ones advance one place in the series; this system of operation in counter-current allows a better taking advantage of the absorbant capacity of the carbon. The alimentation can be put into effect in a descending form, making the solution percolate through a fixed bed of carbon, or ascending, passing the solution in an appropriate velocity to mantain the particles in bed suspended or fluidized.the adsorption in a fixed bed requires a lower quantity of carbon than the fluidized system, but it is limited to operate only with clarified solutions and in a specific flux of no more than 2 lt/min. by dm2 of section.

This last one, on the other hand, can function with turbulent solutions and in a flux which, for thick carbons as the – 6/ + 16 wire metting, can reach up to 10(lt/min)/dm2.