Optimization of ammonia nitrogen removal by SO42− intercalated hydrotalcite using response surface methodology

Abstract

SO₄²⁻ intercalated Mg–Al hydrotalcite (S-LDH) was prepared under microwave irradiation and characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The S-LDH had a typical layered structure containing SO₄²⁻ anions, and intercalation of SO₄²⁻ into the interlayer spaces caused reduction of crystallinity and crystal sizes compared to the Mg–Al hydrotalcite precursor. Furthermore, the Box–Behnken design, an experimental design for response surface methodology (RSM), was used to study the NH₃–N removal by S-LDH under microwave irradiation. The parameters including S-LDH amount, irradiation time, temperature and initial pH were optimized by RSM. From the analysis of variance, it was found that RSM could be used effectively to model and improve the NH₃–N removal efficiency. The optimum conditions were 1.0 g L⁻¹ of the S-LDH, 9.0 min, 70 °C and initial pH 10.0 to achieve 90.4% of the NH₃–N removal rate. Overall, the S-LDH showed a high performance under moderate operating conditions for NH₃–N removal.