Abstract
Charge screening and adsorption capacity of monovalent ions onto pyrite (Py) in aqueous suspensions and the effect of potassium amyl xanthate (PAX) has been studied by measuring the changes in zeta potential (zp) versus pH with streaming potential. PAX addition in the absence of salts leads to an increase in |zp| suggesting dissolution of the surface ferric hydroxides and recovery of bare Py, corroborating existing theories. In the presence of salt, addition of PAX at pH > 6, for which hydroxides interference in not expected, has little effect over the zp, except when Li is present. The water network around the polar head of PAX is expected to be similar to that of hydrated Li+ facilitating the linkage between them and, thus, the formation of Li-mediated Py–PAX bridges. We speculate that these bridges lead to a xanthate shield around anionic sites on Py, decreasing |zp|. An increased PAX dose amplifies the effect of Li as a Py activator but only at low salt. At high salt concentrations, >0.01 M, PAX molecules do not find room to percolate to the surface of Py. Results for monovalent cations should improve our understanding of copper flotation processes in the presence of Py in saltwater.
Highlights
The use of seawater in mining processes is becoming mandatory in regions where freshwater is scarce
Pyrite oxidation and collector adsorption have long been studied and the literature is full of important contributions [2,3,4,5,6,7,8,9,10,11,12,13,14,15]
Pyrite exposed to deuterated water (D2 O) alone shows no evidence of oxidation products on its surface, in air or aqueous solution, pyrite becomes rapidly oxidized forming hydrophilic oxide/hydroxides and hydrophobic iron-deficient sulfide surfaces [16,17,18,19]
Summary
The use of seawater in mining processes is becoming mandatory in regions where freshwater is scarce. The need for water is so great that the use of seawater is decided long before having a fair comprehension of the effects of the various electrolytes and the buffer condition of seawater in the processes involved, in pyrite flotation [1]. This negative potential is thought to be a consequence of a sulfur-rich surface with an iron-deficient sulfide lattice. Pyrite exposed to deuterated water (D2 O) alone shows no evidence of oxidation products on its surface, in air or aqueous solution, pyrite becomes rapidly oxidized forming hydrophilic oxide/hydroxides and hydrophobic iron-deficient sulfide surfaces [16,17,18,19]. The hydrophilic species prevent significant flotation without the addition of collector, which is verified by the easy flotation that is obtained when complexing surface iron with EDTA in solution [10,19]. In a mildly acidic solution, a soluble iron product is Minerals 2019, 9, 584; doi:10.3390/min9100584 www.mdpi.com/journal/minerals
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