The role of surfactants in the leaching of zinc sulphide minerals at temperatures above the melting point of sulphur
Creators: name: Owusu, George
Publisher: name: University of British Columbia
Year: 2008

description: The role of the surfactants lignin sulfonic acid, cocoamido hydroxyl sulfobetaine (CAHSB), tallow amido hydroxyl sulfobetaine (TAHSB), cocoamido betaine (CAB), naphthalene sulfonic acid-formaldehyde condensates and orthophenylene diamine (OPD) in the liquid sulfur-aqueous zinc sulphate-zinc sulfide mineral system has been studied. The effect of the various surfactants on the liquid sulfur-aqueous system interfacial tensions and the liquid sulfur-mineral contact angle were measured in a high temperature-high pres-sure apparatus. In the absence of any surfactant, the liquid-liquid interfacial tension measured 54±1 mN/m, and the liquid sulfur-mineral contact angle was 80±5°. In the presence of 0.3 g/L lignin sulfonic acid, the interfacial tension decreased to about 29±1mN/m; the interfacial tension was not sensitive to any further increase in the surfactant concentration. The contact angle measured 145±5° in the presence of 0.07-0.3 g/L of the surfactant. The presence of OPD in the solution did not have any effect on the liquid sulfur-aqueous solution interfacial tension but increased the contact angle to about130±5°. At a concentration of 0.1 g/L, naphthalene sulfonic acid-formaldehyde con-densates decreased the interfacial tension to 21±1 mN/m. Beyond this concentration, the liquid-liquid interface was not sensitive to any further increase. The contact angle increased to 155±5° even at concentrations as low as 0.05 g/L. CAHSB exhibited just about the same efficiency as lignin sulfonic acid. TAHSB and CAB required higher concentrations in order to effect any substantial changes in the liquid sulfur-aqueous solution interfacial tension. They also effected a contact angle increase to 135±5°. With the exception of OPD, all the surfactants adsorbed at both the liquid-liquid and aqueous-solid interfaces. OPD, on the other hand adsorbed at only the aqueous-solid interface. When introduced into leaching systems, the surfactants influenced the metal extraction to different extents. OPD and lignin sulfonic acid were the most efficient surfactants (or dispersants for liquid sulfur). The extent of zinc extraction was enhanced to about94 % for lignin sulfonic acid and over 99 % for OPD under both low or high pulp density conditions. The other surfactants were unable to enhance zinc extraction even under low pulp density conditions. Application of metaphenylene diamine as dispersant for liquid sulfur under both low and high pulp density leaching conditions resulted in zinc extractions in excess of 98 %. A combination of the interfacial studies and the leaching experiments indicates that the most important characteristic for any effective surfactant under pressure leaching conditions is for the surfactant to adsorb at the aqueous phase-solid interface and increase the liquid sulfur-mineral contact angle. Infrared spectral analysis of both sphalerite leach residue and pulped sphalerite indicates that the lignin sulfonate ions are adsorbed both physically and chemically by the mineral. The chemically adsorbed species form a Zn(II)-based complex that has an organic portion similar to the bulk surfactant structure. OPD, on the other hand, is adsorbed chemically through the interaction of the C-N functional group with the metal ions forming a metal-amine complex.