Highly selective adsorption of nitrates and phosphates in industrial secondary effluent using modified resin and resin recycling

The advanced treatment and resource recovery of nitrogen (N) and phosphorus (P) in water are important environmental concerns within water pollution control. This study synthesized a series of anion-exchange resins with quaternary ammonium groups featuring varied alkyl chains. Additionally, hydrated lanthanum oxide (HLO) was generated in situ within the pore structure of the resin. The adsorption selectivity of the modified resin for nitrates and phosphates in water was systematically investigated. Upon HLO loading, the specific surface area of the resin increased, the average pore size decreased, and the mechanical strength of the resin increased. This new resin exhibited a wide pH range and maintained high selectivity for nitrates and phosphates at highly competitive ions and humic acid concentrations. The difference in adsorption capacities between original and HLO-loaded resins for phosphates increased with increasing N/P ratio of the solution. For instance, the adsorption capacity of L10-La for phosphates exceeded that of L10 by 1.8 times in a sole phosphates environment, increasing to 19 times when the N/P ratio reached 25. Post-saturation, the HLO-loaded resin efficiently regenerated through a 15 % NaOH/5 % NaCl binary solution. Moreover, LaPO 4 , formed during the adsorption process within the resin channel reconverted into HLO, thus restoring the adsorption efficacy of La-loaded resin for phosphates. The deep purification and recycling of N and P in industrial secondary effluent facilitated by the new resin adsorption material described in this study holds significant promise in conserving water resources and controlling water pollution in the future. • Resin with triethylamine quaternary ammonium groups exhibited high selectivity for nitrates. • Hydrated lanthanum oxide (HLO)-loaded resin exhibited significant selectivity for phosphates. • HLO loading increased the specific surface area and mechanical strength of the resin. • Humic acids exerted no effect on the adsorption of nitrate and phosphate by HLO-loaded resin. • NaOH–NaCl binary solution facilitated efficient regeneration and reuse of HLO-loaded resin.