Recycling of high-purity simonkolleite from electroplating wastewater via a coupled PAC coagulation and hydrothermal separation route

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College of Forest Resources and Environmental Science


Polyaluminium chloride (PAC) is a common flocculant that precipitates heavy metals from electroplating wastewater but is involved in the mass production of hazardous sludge. The conventional method of recovering heavy metals from sludge is tedious and heavily consumes extractant. Herein, we developed a facile strategy to effectively recycle heavy metals from electroplating wastewater effluent. The strategy included five steps. Firstly, wastewater with 87.4 mg/L Zn was collected from the effluent of an electroplating workplace and subjected to PAC coagulation to produce a brownish sludge. Secondly, the sludge was leached by 2.4 M nitric acid and 2.2 M hydrochloric acid to produce an acid solution with 18.4 g/L Ca, 2.7 g/L Al and 6.3 g/L Zn, where Ca and Al were the major impurities from the commercial PAC product. Thirdly, more than 97% Ca was precipitated as gypsum prior to the separation of Al and Zn by adding 0.6 M Na2SO4 with Al/Zn loss < 3%. Fourthly, 99.5% Al was hydrothermally crystallised as a mixture of hydrobasaluminite and boehmite with Zn loss < 0.8% through the addition of L-ascorbic acid. However, Al removal efficiency reached only 41.2% without ascorbic acid. Fifthly, 99% Zn was recycled as simonkolleite with a composition of 60.3% ZnO, 0.1% Al and 0.5% Ca after the remaining solution was adjusted to pH 7.3. The developed route effectively enriched Zn from electroplating wastewater and recovered Zn as simonkolleite with gypsum and hydrobasaluminite as the by-products. Accordingly, the route reactivated the PAC coagulation process in the treatment of electroplating wastewater.

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Journal of Water Process Engineering