Thermodynamic and kinetic studies of galena in the presence and absence of potassium ethyl xanthate

A study of the electrochemistry of the PbS-H₂O and PbS-KEX-H₂O systems has been made by carrying out thermodynamic calculations, electrochemical experiments and microflotation tests. Particular attention has been paid to how well this system can be described by equilibrium thermodynamics. The thermodynamic calculations are more comprehensive than previous ones of this type since they are based on a mass balance which includes both insoluble and soluble species. The data they provide include equilibrium concentrations of all dissolved species at any E_h and pH and an E_h-pH stability diagram for each collector addition. Also, two- and three-dimensional plots showing the effect of E_h and pH on xanthate uptake by the galena surface have been presented for the first time. These are particularly useful because they can be directly compared to observed flotation data. The results of voltammetry, IGP and potential-step experiments suggest that the oxidation of galena at pH 6.8 and 9.2 begins at a potential below the value predicted by bulk thermodynamics with the electrosorption of OH⁻ and the formation of a metal-deficient sulfide and a surface lead oxide. When oxidation becomes extensive enough, bulk products, Sº and PbO, begin to nucleate. Thiosulfate is detected at pH 9.2, but only becomes significant at high potentials. The electrochemical experiments indicate that xanthate adsorbs onto galena via a one-electron transfer chemisorption reaction in the first monolayer and via the formation of PbX₂ in subsequent layers. It also appears that galena oxidation and xanthate adsorption are competitive processes that tend to inhibit each other. Ground galena exhibits natural floatability at pH 9.2 as long as oxidation extends to the formation of a metal-deficient sulfide, but not to bulk PbO. When 10⁻⁵ M xanthate is added, the upper potential limit for flotation agrees well with the value predicted from thermodynamics for the decomposition of PbX₂. The lower limit, on the other hand, is at least 200 mv lower than any of the predicted values. PbS dissolves anodically at pH 1.1 and 4.6 to form Pb²⁺ and Sº first by a random surface process and then by a nucleation and growth mechanism once oxidation becomes extensive enough. At pH 0, the relation between the open-circuit potential and mineral solubility, as predicted by the thermodynamic calculations, agrees quantitatively with that determined experimentally. However, as the pH is increased to 1.1 and 4.6, the system becomes increasingly less reversible.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Materials Engineering Science

Department dc:contributor.department

Materials Engineering Science

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1985

Author dc:creator

• Pritzker, Mark David

Chair dc:contributor.committeechair

• Yoon, Roe-Hoan

Committee members dc:contributor.committeemember

• Gibbs, Gerald
• Reifsnider, Kenneth L.
• Richardson, P.E.
• Sanzone, George
• Ward, Thomas C.
• Wightman, James P.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/76476

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/76476