Efficient low-concentration phosphate removal from sub-healthy surface water by adsorbent prepared based on functional complementary strategy

Abstract

The remediation of low-concentration phosphorus polluted surface water (LP-SW) is one of most challenging environmental issues worldwide. Adsorption is more suitable for LP-SW remediation due to its low cost and operability. Based on the strategy of functional complementation among industrial solid wastes (ISWs), ISW-based phosphate absorbent material (PAM) was prepared from coal ash (CA, binder), rich‑calcium (Ca) carbide slag (CS, active component) and iron salt (functional reagent) by optimizing materials ratios and roasting conditions. PAM prepared under optimal conditions (Fe/CC-2opt) had good phosphate adsorption efficiency. Notably, Fe/CC-2opt not only ensured that the effluent met Environmental Quality Standards for Surface Water (pH = 6.0–9.0), but also facilitated the formation of brushite instead of hydroxyapatite due to FeSO4 addition. Compared with hydroxyapatite, brushite had greater potential application value as fertilizer due to its solubility and high P/Ca ratio. The possible mechanisms of phosphate adsorption by PAM included surface precipitation, surface complexation, electrostatic adsorption and release of Ca2+/OH−. Preparation cost of PAM was 80 US$/ton, and treatment cost was 0.07 US$/g P. Regeneration efficiency of PAM was still above 80 % after five cycles. The design idea and result of this study provide theoretical basis and technical support for the preparation of PAM with low cost, commercial production and great adsorption capacity.