Enhanced performance of calcium-enriched coal ash for the removal of humic acids from aqueous solution

• The adsorption and coagulation characteristics of HA in aqueous solution has been examined.
• A shell-added DTs is markedly superior to PACs for HA removal.
• The presence of anhydrite and lime in DTs dramatically increases HA removal.
• Low solution pH and high DTs dosage are favorable for the removal of HA.
• There is an optimal temperature of approximately 313 K for the HA removal by DTs.

This study is designed to follow-up our previous work, in which we demonstrated synergistic and in-situ desulfurization effects during co-disposing shell wastes and an aqueous condensate (AQ) derived from biomass carbonization in combination with coal combustion. The potential use of Ca-enriched coal ash as a coagulant for removing humic acid (HA) from aqueous solution is explored in this study. The HA removal performance of raw and shell-added Datong (DT) coal ashes from aqueous solution is examined and compared with that of commercial aluminum sulfate (alum) and powdered activated carbons (PACs). It is found that shell-added DT ash (DTs) is markedly superior to both PACs and raw DT ash (DTr) and is even comparable to alum in terms of HA removal. The excellent HA removal performance of DTs was mainly attributable to the formation of anhydrite and lime during coal combustion. The removal efficiency of HA strongly depends on temperature, initial pH, and DTs dosage. From the results obtained in this study, it is revealed that the calcium-enriched coal ash can be used as an efficient and cost-effective coagulant to treat surface and/or waste waters that are polluted with humic substances.

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