Optimization of layered double hydroxide stability and adsorption capacity for anionic surfactants

Abstract

Low cost adsorption technology offers high potential to clean up laundry rinsing water. From an earlier selection of adsorbents (Schouten et al. 2007), layered double hydroxide (LDH) proved to be an interesting material for the removal of anionic surfactant, linear alkyl benzene sulfonate (LAS) which is the main contaminant in rinsing water. The main research question was to identify the effect of process parameters of the LDH synthesis on the stability of the LDH structure and the adsorption capacity of LAS. LDH was synthesized with the co-precipitation method of Reichle (1986); a solution of M2+(NO3)2 and M3+(NO3)3 and a second solution of NaOH and Na2CO3 were pumped in a beaker and mixed. The precipitate that was formed was allowed to age and was subsequently washed, dried and calcined. The process parameters that were investigated are the concentration of the initial solutions, M2+/M3+ ratio and type of cations. The crystallinity can be improved by decreasing the concentration of the initial solutions; this also decreases the leaching of M3+ from the brucite-like structure into the water. The highest adsorption capacity is obtained for Mg2+/Al3+ with a ratio 1 and 2 because of the higher charge density compared to ratio 3. Storing the LDH samples in water resulted in a reduction of adsorption capacity and a decrease in surface area and pore volume. Therefore, LDH is not applicable in a small device for long term use in aqueous surroundings. The adsorption capacity can be maintained during storage in a dry N2 atmosphere.