Optimum condition for the removal of Cr(VI) or total Cr using dried leaves of Pinus densiflora

► Mechanism of Cr(VI) biosorption by P. densiflora was 'adsorption-coupled reduction'. ► Optimum condition for Cr(VI) or total Cr removal was obtained through RSM. ► 100% of Cr(VI) and > 95% of total Cr was removed at pH 4 and 40 °C.