Mg/Al LDH Enhances Sulfate removal and Clarification of AMD Wastewater in Precipitation Processes
Paulina Maziarz1, Jakub Matusik2, Tiina Leiviskä3
1Department of Mineralogy, Petrography and Geochemistry; Faculty of Geology, Geophysics and Environmental, Protection; AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Krakow, Poland. pmaziarz@agh.edu.pl.
Abstract:
The sulfate removal from acid mine drainage (AMD) water (initial concentration: 5301 mg/L) was investigated by precipitation and/or adsorption using calcium hydroxide (Ca(OH)2) and synthetic layered double hydroxide (LDH) of the Mg/Al type. The exclusive use of LDH efficiently removed sulfates (64.2% reduction); however, alteration of its structure was observed due to low pH. The use of Ca(OH)2 in different doses calculated in relation to gypsum stoichiometry allowed to achieve an 86% removal of sulfates. Depending on the equilibrium pH, gypsum or ettringite were the main identified phases. The two-step removal, involving the use of Ca(OH)2 followed by LDH, was less efficient than the use of the Ca(OH)2/LDH mixture when the stoichiometric amount of Ca(OH)2 in relation to gypsum was applied. The application of mixture resulted in a fast pH increase, which prevented destruction of the LDH structure. Most importantly, the use of mixture significantly reduced the sludge volume and enhanced its settling velocity.
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