Dealumination of clinoptilolite and its effect on zinc removal from acid rock drainage

•Clinoptilolite dealumination was observed during acid drainage treatment.•Unit Zn uptake on Al-colloid was significantly higher than on clinoptilolite particles.•Hydrolysis of aluminum species and formation of colloids likely occurred.•Co-precipitation of Zn by Al-colloids is examined for various aqueous pHs.

Clinoptilolite, a natural zeolite, is capable of removing heavy metals from acid rock drainage (ARD). Previous studies have neglected the dealumination of clinoptilolite and its impact during remediation. This study observed the dealumination of clinoptilolite during ARD remediation in a slurry bubble column (SBC), and investigated its impact on the capture of zinc.Uptake tests were performed with natural ARD and various sorbent average particle diameters from 300 to 1400 μm, superficial gas velocities from 0.08 to 0.23 m s−1, initial aqueous pH from 2 to 6, Zn concentrations from 15 to 215 ppm and sorbent/solution mass ratios from 25 to 400 g kg−1 to test zinc uptake. Dealumination of clinoptilolite was sometimes observed during the uptake process. Increased Al in the aqueous phase led to co-precipitation of Zn-Al colloid, enhanced by abundant sulfate in solution. The unit zinc uptake of the Al colloid was found to be much higher than for the raw clinoptilolite.