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Gold-Paraffin process
A process called Gold-paraffin is under development to recover gold from gravity concentrates or fresh ores. The process should be simple enough to be used as an alternative to amalgamation. The process is based on the selective adhesion of liberated gold particles to hydrophobic materials and their separation from a pulp of the ore (like mercury in amalgamation). As a main advantage, this process is not deleterious to the environment, since hydrophobic material used is paraffin-wax, extremely used in the food and pharmaceutics industries.
In bench scale, the process is carried out heating a 25-30% solids pulp of the ore to a temperature 2 oC higher than the melting point of the paraffin-wax used (approx. 68 oC), at this temperature a certain amount of paraffin is added and let melt. After melting, a stirrer motor is turned on to disperse the paraffin and allow it to be in contact with the ore. The gold selectively adhered to the paraffin-wax is transferred to the paraffin phase after the agitation is stopped. After cooling, at room temperature, the paraffin (S.G. 0.8) is a floating solid and then can be removed and treated to recover the gold contained in it.
The theoretic viability of the process was analyzed based on the work of Jacques et.al. (1), these authors studied the feasibility of a solid particle (phase 1) be transferred from one liquid (phase 3) to other one (phase 2), in a system of a solid and had two immiscible liquids, where one liquid (phase 2) wets preferently the solids particles (phase 1). The two states, initial (I) and final (II) are presente
d in the figure.
By analyzing the free energy and the forces taking part in the interface, Jacques obtained an expression for the difference of free energy of states II-I as a function of the three phase contact angle, θ (measured in phase 2, paraffin), and the ratio of the dispersed liquid droplet radius to the particle radius (n = r2 / r1). The most stable state is the one with the lowest free energy, which implies a three phase contact angle θ < ¶/2 and n → ∞, for the separation to occur (state II).
Figure shows Process of particle (phase 1) distribution from continuous liquid (phase 3) into dispersed liquid (phase 2), showing phase relationship between initial state I and final state II configurations (1).
