7, the maximum removal of Cr(VI) by CATCS was at pH = 5, which implied the CATCS flocculant trended to adsorb Cr(VI) in form of HCr[O.sup.-.sub.4].
where [q.sub.e] (mg/g) is the amount of Cr(VI) adsorbed on per unit weight of CATCS, [C.sub.e] (mg/L) is the equilibrium concentration of Cr(VI), [Q.sub.L] (mg/L) is the maximum monolayer adsorption capability, [K.sub.L] (L/mg) is a constant related to the free energy of adsorption.
It was evident from these data that the surface of CATCS was made up of homogeneous and heterogeneous adsorption patches.
The negative [DELTA]G implied the process of Cr(VI) removal by CATCS was spontaneous.
The kinetic curves of Cr(VI) removal by CATCS at various temperatures are shown in Fig.
where [q.sub.t] (mg/g) and [q.sub.e] (mg/g) are the amounts of Cr(VI) adsorbed onto the CATCS at time t and equilibrium, [k.sub.1] ([min.sup.-]) is the adsorption rate constants.
The kinetic parameters for Cr(VI) adsorbed onto the CATCS were summarized in Table 4 and the fitting plots of pseudo-first order kinetic model and pseudo-second order equation were shown in Figs.
The activation energy of Cr(VI) absorbed onto CATCS was determined using the Arrhenius equation  Eq.
The activation energy ([E.sub.a]) of the adsorption process of Cr(VI) by CATCS was 29.16 kJ/mol, which indicated the existence of chemisorptions mechanism.
A copolymer flocculant CATCS derived from starch and chitosan was synthesized and applied for the removal of Cr(VI) from aqueous solution.