Adsorption of arsenic, chromium and uranium from saline water on clinoptilolite and the treatment of the spent regenerants by duffusion dialysis
Among various water purification and recycling technologies, adsorption is a fast, inexpensive and universal method. The development of low-cost adsorbents has led to the rapid growth of research interests in this field. The objective of this present study is the optimization of process parameters in adsorption of arsenic, chromium and uranium ions. The adsorption behavior of natural zeolite (clinoptilolite) has been studied in order to determine its applicability in treating water containing arsenic, chromium and uranium. The multiple adsorption of arsenic As (V), trivalent chromium Cr (III)] and uranium (VI) on natural zeolite (clinoptilolite) in single component and multiple component systems has been studied. The optimum conditions for the treatment process were investigated by observing the influence of pH, time, adsorbate concentration, the presence of competing ions and the effect of sodium chloride (NaCl) on metal ions adsorption by natural zeolite. The adsorption of arsenic, chromium and uranium by clinoptilolite was studied under batch and column experiments. The adsorption of the metals was evaluated using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The data were interpreted with an adsorption model, in which a linear relationship was employed to express the equilibrium relationship using Langmuir and Freundlich models. According to the equilibrium studies, the adsorption selectivity sequence in both single and multiple systems can be given as Cr > U > As. The Freundlich equation was the most suitable adsorption model for the adsorption equilibrium data with R2 values of 0.96, 0.96, and 0.95 for As, Cr, and U respectively. The adsorption studies showed low affinity by clinoptilolite for the removal of Arsenic (37.2%) compared to both chromium (88.6%) and uranium (87.5%) at initial maximum concentration of 1000 (µg/L) in the multiple component adsorption system. The presence of sodium chloride increased the adsorption rates of the clinoptilolite. In the single component adsorption the maximum percent adsorption of As, Cr and U were 38.3%, 87.8% and, 85.2% respectively and in the binary metal mixtures the maximum percent adsorptions of As, Cr and U were 34.8%, 87.3%, and 82.6 % respectively at an initial concentration of 1000 µg/L. This was no significant difference when the metals were in a single component system or in a binary mixture. The breakthrough curve analysis was determined using the experimental data obtained from the continuous adsorption column experiment. The chromium and uranium had a break-through time of 25 h and 21 h, respectively, while arsenic had an instant breakthrough from the zeolite. Regeneration of the zeolite was carried out with hydrochloric acid to reduce the sludge produced and for economic benefits. The spent acid was recovered with an anion-exchange membrane by diffusion dialysis. The result obtained indicates high performance of the diffusion dialysis with 77% HCl recovery, 94% chromium ion rejection and 71.7% uranium rejection. The anion-exchange membrane by diffusion dialysis was not effective in the rejection of arsenic. It has 0% rejection, which is an indication of a negative charged arsenic complex formed. Clinoptilolite natural zeolite proved to be a good adsorbent for removing chromium and uranium but not arsenic. Diffusion dialysis with an anion-exchange membrane effectively recovers acid from the spent regenerant waste stream.
Civil engineering|Environmental engineering
Tanimola, Mutiu Olaitan, "Adsorption of arsenic, chromium and uranium from saline water on clinoptilolite and the treatment of the spent regenerants by duffusion dialysis" (2013). ETD Collection for University of Texas, El Paso. AAI1551586.