Ph.D. Natalia Petrovskaya: FUNDAMENTALS OF SORPTION OF FLOTOREAGENTS By Ph.D. Natalia Petrovskaya

Tuesday 7 November 2017

FUNDAMENTALS OF SORPTION OF FLOTOREAGENTS By Ph.D. Natalia Petrovskaya

Sorption of flotation reagents at interfaces occurs spontaneously and is accompanied by a loss of free surface energy. Changing the standard free energy Gibbs ΔG⁰ in the sorption of flotoreagents at the interface is described by Gibbs [1].
For the thermodynamic probable processes accompanied by energy loss, the value of Gibbs free energy ΔG⁰ should have a negative value.

Example 1. On the surface of pyrite FeS₂ there is the surface compound of ethyl xanthate of iron Fe(C₂H₅OCSS)₂. The surface compound is formed as a result of chemical sorption and it consists of ethyl xanthate anions C₂H₅OCSS^- and iron cations Fe²⁺. Can hydroxyl ions OH^- to displace from the surface of pyrite the anions of ethyl xanthate C₂H₅OCSS^- and to form the new surface compound of ferric hydroxide Fe(ОН)₂ as a result of chemical sorption?
Since ΔG⁰ is negative, the flow of this process is thermodynamically probable. This reaction is used for the depression of pyrite by lime. The results of the practice argue that, with the chemical sorption of xanthate, poorly soluble compound of xanthate of iron Fe(C₂H₅OCSS)₂is formed on the surface of pyrite. This compound can be removed from the pyrite surface only with using its displacing by the hydroxyl ions, which are actively interact with the iron cations Fe²⁺ to form ferric hydroxide Fe(ОН)₂.
Example 2. You should assess the thermodynamic probability of the film formation of lead sulfide PbS on the surface of cerussite PbCO₃ after exposure of sodium sulfide Na₂S.

Since ΔG⁰ is negative, the flow of this process is thermodynamically probable. This reaction is used in sulphidation of oxidized lead minerals (PbCO₃).
Example 3. You should assess the thermodynamic probability of sorption of copper cations Cu²⁺ on sphalerite ZnS.
Since ΔG⁰ is negative, the flow of this process is thermodynamically probable. This reaction is used to activate sphalerite by copper sulfate.
Example 4. You should evaluate the thermodynamic probability of sorption of ethyl xanthate on the unoxidized (unmodified) surface of galena:

Since ΔG⁰ is positive, the flow of this process is thermodynamically incredible. This is confirmed by the practice of the flotation. The mineral surface should be partially oxidized to fix the xanthate. This is imperative.
Example 5. You should rate thermodynamic probability of xanthate sorption after the partial oxidation of the surface of galena:
Since ΔG⁰ is negative in both cases, the flow of this process is thermodynamically probable. The mineral surface should be partially oxidized to fix the xanthate.
Example 6. You should rate thermodynamic probability of the oleic acid fixing on the surface of fluorite CaF₂: