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Acid rock drainage remediation with Bear River clinoptilolite in a slurry bubble column

University of British Columbia

Clinoptilolite, a natural zeolite, is capable of removing heavy metals from acid rock drainage (ARD). However, previous studies have predominantly been on artificial solutions, with no previous work on sorbent regeneration. This study investigated a novel process for capturing ARD and regenerating clinoptilolite based on a slurry bubble column (SBC) for enhanced mass transfer. Uptake tests were performed with natural ARD and various sorbent particle sizes from 300 to 1400 μm in average diameter, superficial gas velocity from 0.08 to 0.23 m/s, initial aqueous pH from 2 to 6, Zn concentrations from 15 to 215 ppm and sorbent/solution ratio from 25 to 400 g/kg to test zinc uptake. To obtain favorable regeneration, zinc in loaded clinoptilolite was displaced by NaCl as regenerant. Regenerant concentrations from 10 to 40 g/kg, regenerant/sorbent ratios from 100 to 400 g/kg, particle sizes from 300 to 1400 μm, and initial regenerant pH from 2 to 6 were tested to find suitable regeneration conditions. To test the long-term viability of clinoptilolite sorbent, repeated capture-regeneration cycles were tested. It was shown that NaCl regenerant could be reused to minimize waste volume. Three removal-only cycles after 10 full cycles continuously decreased the accumulated zinc in the clinoptilolite, allowing the uptake capacity to be almost fully recovered. When 10 full cycles were tested after three removal stages, results were similar to those for the first 10 cycles. Only one-quarter of the regenerant was required to achieve a similar total zinc uptake when reused NaCl solution was utilized. During the remediation, dealumination of clinoptilolite was observed, under certain circumstances. 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 much higher than that of the raw clinoptilolite. Adsorption isotherms were fitted to the Langmuir model, and the overall aqueous species and surface uptake were explored by the PHREEQC model. The cyclic capture/regeneration process is promising that further development work is warranted.

Text

2013-07-04

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/44625

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/