Abstract
FeMgMn-LDH, a type of potential environmental remediation material, has been synthesized via a co-precipitation method, and its adsorption characteristics for nitrate were investigated in this study. It’s shown that the prepared FeMgMn-LDH is a promising adsorbent for anions removal, which has high buffer capacity (final pH remained between 9 and 10) and high reversibility, and can remove nitrate ions selectively though an anion-sieve effect. The maximum amount of nitrate adsorption is 10.56 N-mg g−1 at 25 ℃. The removal rate of nitrate ions can reach 86.26% with the adsorbent dose of 5 g/L in a real water. The competition order of coexisting anions on nitrate adsorption by FeMgMn-LDH is CO32− > PO43− > SO42−. The negative values of ΔG0 (from − 27.796 to − 26.426 kJ mol−1) and ΔH0 (− 6.678 kJ mol−1) indicate that the nitrate adsorption process on the FeMgMn-LDH is spontaneous and exothermic. The main adsorption mechanisms of nitrate removal from aqueous solutions by FeMgMn-LDH are electrostatic attraction and ion exchange.
Highlights
Excess nitrate in aquatic environment have become a serious human health risk
A clean and stable preparation process was assured because the molar ratio of Fe/Mg/Mn in FeMgMnLDH was approximately equal to that in the mixed metal solution, which was used for co-precipitation
From the pore size distribution curve, the main pore diameter of FeMgMn-layered double hydroxides (LDHs) is distributed in the range of 7 nm to 23 nm, and average pore diameter is about 38.21 nm
Summary
Excess nitrate in aquatic environment have become a serious human health risk. High nitrate concentration in drinking water may lead to m ethemoglobinemia[1] or blue baby syndrome[2,3], which could induce the gastric and intestinal c ancer[4,5]. It is urgent need to develop effective methods and materials to remove excess nitrate from water. Various adsorbents have been investigated, such as activated carbon[17], metal oxide hydroxides, activated alumina, modified zeolite, layered double hydroxides[18,19], slag, fly ash, red mud, crop residues, peat, kaolinite and so on. These kinds of materials are riddled with pore structures, and show high adsorption capacity. The influence of ion concentrations, temperature, pH, and coexisting anions, on nitrate ions removal by FeMgMn-LDH, were all considered in this study
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