Efficient removal of hexavalent chromium from aqueous solutions using autohydrolyzed Scots Pine ( Pinus Sylvestris   ) sawdust as adsorbent

In this work, a low-cost lignocellulosic adsorbent with high biosorption capacity is proposed, suitable for the efficient removal of hexavalent chromium from water and wastewater media. The adsorbent was produced by autohydrolyzing Scots Pine ( Pinus Sylvestris

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) sawdust. The effect of the autohydrolysis conditions, i.e., pretreatment time and temperature, on hexavalent chromium biosorption was investigated using energy-dispersive X-ray spectroscopy (EDS) and UV-visible spectrophotometry. The Freundlich, Langmuir, Sips, Radke-Prausnitz, Modified Radke-Prausnitz, Tóth, UNILAN, Temkin and Dubinin- Radushkevich adsorption capacities and the rate constant values for pseudo-first- and pseudo-second-order kinetics indicated that the autohydrolyzed material exhibits significantly enhanced hexavalent chromium adsorption properties comparing with the untreated sawdust. The Freundlich's adsorption capacity K_F increased from 2.276 to 8.928 (mg g^-1)(L mg^-1)^1/n, and the amount of hexavalent chromium adsorbed at saturation (Langmuir constant q_m ) increased from 87.4 to 345.9 mg g^-1 , indicating that autohydrolysis treatment at 240°C for 50 min optimizes the adsorption behavior of the lignocellulosic material.