Chromium VI adsorption from sodium chromate and potassium dichromate aqueous systems by hexadecyltrimethylammonium-modified zeolite-rich tuff

In the present investigation, zeolite-rich tuff from the state of Chihuahua, which was conditioned with a sodium chloride solution and subsequently modified with a hexadecyltrimethylammonium bromide solution, was used to evaluate the removal of Cr(VI) from aqueous systems prepared with Na2CrO4, K2Cr2O7 or a mixture of both Na2CrO4 and K2Cr2O7 salts. The zeolitic materials were characterized by scanning electron microscopy and X-ray diffraction, and their surface area was also determined. These experiments were performed in a batch system in which the influences of the pH, contact time between phases, and concentration of Cr(VI) in solution on the adsorption of Cr(VI) by surfactant-modified zeolite-rich tuff were investigated. The removal efficiency of chromium ions from aqueous solution is influenced by pH and the specific chromium species involved plays an important role in the adsorption process. The Cr(VI)-Na2CrO4 and Cr(VI)-K2Cr2O7 adsorption kinetics data were fit to a pseudo-second-order model, and the Langmuir isotherm adequately described the experimental results of these mono-component systems. In the Cr(VI)-Na2CrO4:Cr(VI)-K2Cr2O7 mixture, the surfactant-modified zeolite-rich tuff adsorbed more Cr(VI) depending on the initial ratio of Na2CrO4:K2Cr2O7 salts in the bi-component aqueous system.