The mechanism of pyrite depression at acidic pH by lignosulfonate-based biopolymers with different molecular compositions

• The biopolymer structure feature played a significant role in depressing pyrite.
• Molecular weights of the biopolymer determined its adsorption capacity on pyrite.
• Functional groups determined biopolymers’ ability to inhibit collector adsorption.
• Functional groups determined biopolymers’ ability to reduce contact angle of pyrite.
• The counterion Ca2+ enhanced the effect of a biopolymer as a pyrite depressant.

Electrochemical studies, adsorption isotherms and contact angle measurements were conducted to compare the effect of three lignosulfonate-based biopolymers (DP-1775, DP-1777 and DP-1778) as pyrite depressants in flotation at acidic pH. The adsorption isotherms showed that DP-1775 and DP-1778 had a higher adsorption capacity than DP-1777. The contact angle of pyrite particles was reduced by the three biopolymers in the order of DP-1778 > DP-1777 > DP-1775 at a similar adsorbed amount. These results are in accordance with biopolymers’ ability to inhibit collector adsorption in electrochemical studies. The depressing effect of these biopolymers was related to the biopolymer composition. It was found that the biopolymer molecular weight determined its adsorption capability and surface coverage. The content of functional groups was responsible for the change in contact angle. While a higher molecular weight led to greater pyrite depression, calcium ion as a counterion in the biopolymer structure also played a role.