Recycling aluminum from polyaluminum chloride sludge through acid dissolution and cation resin separation/purification.

To recycle aluminum (Al) from waterworks sludge resulting from polyaluminum chloride (PAC) used as coagulants, this study proposed an innovative strong acidic cation (SAC) exchange resin treatment strategy for Al separation from coexisting fulvic acid (FA) and heavy metals (HMs) in the HSO leachate of PAC sludge. Fluorescence titration confirmed the breakdown of the Al-FA complex at pH 2.0, which facilitated Al separation from FA in the acidic leachate. The species distribution of the dissociated Al (i.e. Al, Al, and Al) significantly influenced the adsorption of Al onto the cation exchange resin. The continuous release of H during the cation exchange reaction greatly promoted the transformation of dissociated Al and Al into Al, thereby improving the adsorption of total Al. Moreover, the SAC resin column successfully separated the codissolved HMs from the Al in the leachate even at an influent pH of 2.8, which was attributed to the greater selectivity of the sulfonate groups on the cation exchange resin for free Al. The Al eluted from the exhausted resin with 1.1 M HSO was collected as the recycled coagulant after proper pH adjustment. The Al adsorption capacity of the SAC resin decreased by approximately 5 % with each operation cycle and was regained by complete regeneration with 1.8 M HSO after 5 cycles. Overall, the integrated efficiency of Al recovery from PAC sludge by HSO acidification and SAC resin separation/purification reached 70.10 %. The recycled Al from sludge has a water treatment performance comparable to that of fresh PAC coagulant.