Optimized molecular length and uniform molecular weight distribution enhance depression effect of macromolecular depressant towards serpentine

Nickel is an extremely important strategic metal resource. However, in the flotation of nickel sulfide ores, serpentine causes a decline in the grade of nickel concentrate due to heterocoagulation and mechanical entrainment. Organic polymers represent prevalent depressant choices for serpentine. Typical synthetic polymer depressants are usually prepared via conventional free radical polymerization, but synthesized depressants exhibit significant defects: broad molecular weight distribution and uncontrollable molecular structure, which markedly reduce the depression effectiveness. To address these challenges, this study proposes, for the first time, the use of reversible addition-fragmentation chain transfer (RAFT) polymerization to precisely design and synthesize an ABA-type triblock copolymer depressant from acrylamide and acrylic acid. Through systematic comparison with a random copolymer of acrylamide and acrylic acid (RAB) prepared via traditional free radical polymerization, the innovative advantages and mechanisms of the ABA-type depressant in terms of molecular structure, adsorption behavior and flotation performance were elucidated. Experimental results demonstrate that, owing to narrow molecular weight distribution and long molecular chains, ABA forms a dense adsorption layer on the serpentine surface. Through chelation of carboxyl groups with Mg²⁺ and hydrogen bonding, ABA significantly enhances surface hydrophilicity and reverses the surface charge of the serpentine, effectively inhibiting heterocoagulation between serpentine and pentlandite and increasing the macroscopic size of fine serpentine particles. This study provides a novel strategy for the design of high-performance macromolecular depressants targeting magnesium silicate gangue in complex nickel ore flotation, overcoming the technical limitations of traditional depressants and demonstrating significant industrial application value.