Flotation in Seawater

Abstract

A classification of flotation processes carried out in concentrated electrolyte solutions, e.g., seawater, is proposed using the most obvious features of these processes: low or high content of Mg²⁺ and Ca²⁺ ions, pulp ionic strength, and pH. The first distinguishable group is the processes carried out in NaCl/KCl solutions, about 0.5 M in the case of salt flotation of inherently hydrophobic minerals, and at concentrations about 10 times higher in the flotation of potash ores. In the flotation of sulfide ores, such as nickel or copper ores, with xanthate-like collectors, the xanthate collector is apparently not affected by pulp ionic strength and only adjustment of frother may be required. Content of Mg²⁺ and Ca²⁺ ions in seawater is the main difference between such systems and fresh water. The presence of these metallic ions can adversely affect flotation in the pH ranges over which these ions hydrolyse. The successful flotation of Cu-Mo ores typically requires depression of pyrite at high pH values achieved with the use of lime. However, in seawater, flotation of Cu-Mo ores requires removal of the hydrolysis products of the Mg²⁺ and Ca²⁺ ions or the use of a pyrite depressant that can be effective over the pH ranges that are much below the pH of hydrolysis. Mg²⁺ and Ca²⁺ ions also affect flotation of phosphate ores with fatty acids. In this case, the depression mechanism is not caused by precipitating magnesium hydroxides on the mineral surface but by precipitation of collector insoluble salts, and the same ions are responsible for depression in both cases. In the seawater flotation of Cu-Mo sulfide ores and phosphate ores, the practical solution involves either removal of Mg²⁺ and Ca²⁺ ions prior to the flotation or complexation with other reagents.