Background & aim: Considering chromium major risks such as lung and skin cancer, and also sever effects on kidney and liver; present study was conducted to investigate removal of Cr(VI) using zeolite clinoptilolite from aqueous solution.

Methods: Zeolite clinoptilolite with the size of 4 mm was used to remove Cr (VI) from aqueous solution in present study. Potassium dichromate (K₂Cr₂O₇) and double distilled water were used to prepare aqueous solution of Cr(VI). Residual concentrations of Cr(VI) were measured by a spectrophotometer at 540nm.

Results: The results showed that increasing absorbent mass increased removal capacity and equilibrium time. Decreasing pH from 11 to 4 increased and from 4 to 2 decreased chromium removal efficiencies. Optimum time for zeolite contact was 70 min. In overall, pretreated zeolites (nZVI -modified zeolites) had the highest adsorption (i.e.85%) for Cr(VI), however, adsorption rate for untreated zeolites was less than 25%.

Conclusion: In general, the results show that zeolite modified by nZVI is a high efficiency method to remove Cr(VI) from groundwater.