The Cr(VI) ions concentrations were measured according to 1,5-
diphenylcarbazide spectrophotometry using a visible spectrophotometer
at 540 nm. The standard curve of Cr(VI) ions concentration
(y, mg/L) to absorbance (x) is given as: y = 1.3609x 0.0084, the
scope of x is 0–0.8, and the correlation coefficients of the curves is
0.9994.