The use of very low molecular weight polysaccharides as depressants in PGM flotation

Polysaccharides traditionally used in PGM flotation have molecular weights (MW) varying from 150,000 to 600,000 as measured using gel permeation columns (GPC). In recent years polysaccharides at the lower end of the range (MW of 100,000–150,000) have been used effectively. This work evaluates the use of a modified starch depressant with a much lower average MW of 20,000 as a depressant and compares its performance on two Merensky ores to that of depressants currently used in industry, namely guar gum and carboxymethylcellulose (CMC). The UCT batch flotation system was used to assess the performance of the starch as a depressant of naturally floatable gangue (NFG) as well as its effect on sulphide mineral recovery at low and high dosages. Determination of the amount of polymer adsorbed was also done by assessing polymer in solution at various concentrations using the Du Bois method. PGM assays were carried out on one ore sample. Results indicated that this starch is an effective depressant of NFG.