To study the effect of pH, Cr (VI) samples of 20 mg/L concentration were adjusted to pH 1.5–5.0 as previous studies [17,23] have shown Cr (VI) removal to be favoured at low pH. The initial pH adjustment was made by the addition of 1N H2SO4 or NaOH. The flasks were agitated on the orbital shaker for 2 h. Solutions with 20–200 mg/L Cr (VI) were agitated for up to 6 h to determine the effect of initial concentration and contact time on Cr (VI) removal. Kinetic study of Cr (VI) adsorption
on the adsorbent was also conducted based on these observations. The data were fitted to the following pseudo-first order
and pseudo-second order kinetic equations [13]