kinetic and isotherm of hexavalent chromium adsorption onto nano hydroxyapatite

background : hexavalent chromium ( cr (vi)) is an important contaminant in surface and groundwater and its removal from contaminated water and wastewater has received interest in recent years. this study aimed to explain the removal process of cr (vi) from aqueous solution using nano hydroxyapatite (n-hap) as an adsorbent material. methods: cr (vi) removal experiments with the prepared n-hap were carried out as the batch test in 100 ml flask while agitating on the shaker. the influence of ph (3-11), contact time (3-60 min), cr (vi) concentration (1-2 mg/l) and adsorbent dosage (0.025-1 g/l) were explored. three isotherms models and eight kinetics models were used to evaluate the experimental data, respectively. for validation of kinetic and isotherm data, correlation coefficient, sum of square errors (sse) and normalized deviation were used. results: the removal efficiency of cr (vi) was improved an increase in cr (vi) and n-hap concentration. the results best fitted with langmuir model and the pseudo-second-order rate reaction . analysis of data with dubinin–radushkevich isotherm showed that the adsorption of cr (vi) onto synthetic n-hap is a chemisorption process. conclusion: the n-hap as an ecofriendly compound is effective adsorbent for the removal of cr (vi) from aqueous solution . accordingly, n-hap is feasible and promise adsorbent for treating polluted cr (vi) groundwater.