Adsorption of tripolyphosphate from aqueous solution by Mg–Al–CO3-layered double hydroxides

The adsorption of tripolyphosphate anions (P3O105−) from aqueous solution on Mg–Al–CO3-layered double hydroxides (Mg–Al–CO3-LDHs) and its calcined product (Mg–Al–CO3-CLDH) were investigated. Experiments were carried out as a function of contact time, temperature, initial concentration of solution, adsorbent dosage, initial pH of solution and different phosphate species. The results show that the Mg–Al–CO3-LDH and Mg–Al–CO3-CLDH can be used as effective adsorbents for the removal of P3O105− from aqueous solution. The adsorption of P3O105− on Mg–Al–CO3-LDH and Mg–Al–CO3-CLDH are by ion exchange and ‘memory effect’, respectively. The adsorption processes are followed the pseudo-second-order kinetic model. The rate constants are increased with temperature. The activation energy values on Mg–Al–CO3-LDH and Mg–Al–CO3-CLDH are 11.70 kJ mol−1 and 98.40 kJ mol−1. The adsorption data are fitted well with the Langmuir adsorption isotherm equations. The maximum adsorption capacities on Mg–Al–CO3-LDH and Mg–Al–CO3-CLDH from 298 K to 313 K are 34.52–38.00 mg P3O105− g−1, 118.67–132.92 mg P3O105− g−1, respectively. The adsorption capacities are increased with temperature shows that the adsorption processes are endothermic. The removal rate is changed insignificantly for a wide initial pH of 4.0–10.0. The affinity sequences of different phosphate species on Mg–Al–CO3-LDH and Mg–Al–CO3-CLDH are both HPO42− > H2PO4− > P3O105−.