Enhanced flotation of malachite by sulfidization with sodium tetrasulfide and improved reagent control

The sulfidization stage is critical to the recovery of oxidized copper minerals by the sulfidization-flotation method. Two approaches were investigated to increase recoveries--(1) the use of Na;Based on the kinetic studies of sulfidization of malachite with sodium tetrasulfide and sodium sulfide, it was observed that the extent of sulfidization was greater with the former reagent. A significant difference in the surface morphology was observed for malachite treated with these two reagents. With sodium tetrasulfide, a uniform sulfidized coating formed on the particle surface. With sodium sulfide, the surface was coated with loosely adherent precipitates. During sulfidization a number of secondary reactions occurred giving rise to several dissolved oxysulfide ions and colloidal copper species in solution. The extent of secondary reactions was less with sodium tetrasulfide. The dissolved and colloidal species in the sulfidizing residue consumed a substantial amount of xanthate. Such reactions were found to be detrimental to flotation. Studies of contact angle, Hallimond tube flotation, and laboratory mechanical cell flotation indicated that the flotation of malachite was substantially improved by using sodium tetrasulfide compared to sodium sulfide. A polysulfide mixture prepared at low cost was found to enhance the flotation to a similar extent as obtained for sodium tetrasulfide.;Previous studies and plant practice show that careful control of the sulfidizing species is essential for maximizing the flotation recovery. An improved method for monitoring of hydrosulfide ions was developed, in which a gold electrode was used as the sensor. The electrode was cleaned using a specially developed electrochemical cleaning procedure. A comparison of gold, platinum and sulfide ion selective electrodes was made in terms of electrode response time, electrode sensitivity, and reproducibility of the measurements. The response of gold and platinum electrodes in hydrosulfide solutions was interpreted based on a mixed potential theory. The difference in the response was ascribed to their affinity to oxygen. The advantages of using the gold electrode as an Eh sensor in sulfide solutions over the platinum and sulfide ion selective electrodes were discussed.