Elimination of arsenic (III) by adsorption on coal resulting from date pits and activated thermally and chemically

The objective of this study is the valorisation of a lignocellulosic natural residue, date pits, and its application in the removal by adsorption of the arsenic (III) contained in water. The chronological stages in obtaining coal were: cleaning, drying, crushing and finally either a thermal treatment by pyrolysis at 900 °C (CAP1) or a chemical pretreatment with iron oxide of the natural residue followed by carbonisation at 600 °C (CAP2). The choice of iron oxide is based on the fact that arsenic (III) has strong affinities for the hydroxide and oxide of this metal. The characterisation of the carbonaceous matter showed properties comparable with those of many industrially produced coals. Retention tests of arsenic (III) on the two adsorption materials studied gave a maximum capacity of adsorption (at 20 °C and 24 h of contact time) of about 25 mg/g for the chemically activated carbon and 21 mg/g for the thermally activated one. The study of the influence of pH and temperature showed that at neutral pH and ambient temperature (T = 20 °C), the optimal adsorption of arsenic (III) follows quite closely the Langmuir and Freundlich models. The kinetics of adsorption is slow and is of pseudo-second order type.