Removal of sulfate from aqueous solution using Mg–Al nano-layered double hydroxides synthesized under different dual solvent systems
Xiaobo Liu, Shuang Lü, Zhen Tang, Zhaojia Wang, Tianyong Huang
Abstract
Abstract Because of its priority to remove anions, nano-layered double hydroxide (LDH) was incorporated to improve the sulfate attack corrosion resistance of cement-based materials. Herein, the synthesis of high-efficiency LDH for removal of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msubsup> <m:mrow> <m:mtext>SO</m:mtext> </m:mrow> <m:mrow> <m:mn>4</m:mn> </m:mrow> <m:mrow> <m:mn>2</m:mn> <m:mo>−</m:mo> </m:mrow> </m:msubsup> </m:math> {\text{SO}}_{4}^{2-} is necessary. In this study, LDH with different Mg/Al ratios was synthesized under different dual solvent systems (water and ethylene glycol/ethanol/tetrapropylammonium hydroxide). Based on the adsorption experimental results, the LDH synthesized with n (Mg:Al) = 2:1 under water and ethanol solvent systems (ET2.0) exhibits the best adsorption capacity. The d (003) of LDH synthesized with n (Mg:Al) = 2:1 under different dual solvent systems are 0.7844, 0.7830, and 0.7946 nm, respectively. Three LDH belong to LDH- <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msubsup> <m:mrow> <m:mtext>NO</m:mtext> </m:mrow> <m:mrow> <m:mn>3</m:mn> </m:mrow> <m:mrow> <m:mo>−</m:mo> </m:mrow> </m:msubsup> </m:math> {\text{NO}}_{3}^{-} . The results indicated that their surface charges show obvious difference synthesized under different dual solvent systems, which leads to differences in adsorption performance. The adsorption experimental results show that ET2.0 followed pseudo second-order kinetics and Langmuir model. The ET2.0 removed <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msubsup> <m:mrow> <m:mtext>SO</m:mtext> </m:mrow> <m:mrow> <m:mn>4</m:mn> </m:mrow> <m:mrow> <m:mn>2</m:mn> <m:mo>−</m:mo> </m:mrow> </m:msubsup> </m:math> {\text{SO}}_{4}^{2-} through anion substitution and electrostatic interaction and exhibited excellent adsorption rate with the maximum adsorption capacity of 95.639 mg/g. The effects of pore solution anion (OH − , Cl − , and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msubsup> <m:mrow> <m:mtext>CO</m:mtext> </m:mrow> <m:mrow> <m:mn>3</m:mn> </m:mrow> <m:mrow> <m:mn>2</m:mn> <m:mo>−</m:mo> </m:mrow> </m:msubsup> </m:math> {\text{CO}}_{3}^{2-} ) on the removal of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msubsup> <m:mrow> <m:mtext>SO</m:mtext> </m:mrow> <m:mrow> <m:mn>4</m:mn> </m:mrow> <m:mrow> <m:mn>2</m:mn> <m:mo>−</m:mo> </m:mrow> </m:msubsup> </m:math> {\text{SO}}_{4}^{2-} by the ET2.0 are limited.