Starch based depressors for selective flotation of metal sulfide ores

When starch blends with various biogenic L-alpha-amino acids are heated for 6 h in an open vessel, starch esterifies the amino acids and dextrinizes. The water solubility of the dextrins depends on the acid used in the reaction. Because of the poor solubility of dextrins produced on heating starch with either cysteine, arginine, proline, aspartic acid or glutamic acid, crosslinking of the polysaccharide is postulated. Healing produces free radicals, which possesses unpaired electron localized either on the C, N or S atom depending on the amino acid and thermolysis conditions.