Sorption of Cr(VI) onto natural iron and aluminum (oxy)hydroxides: Effects of pH, ionic strength and initial concentration

A Comparative Study on Removal of Hazardous Anions from Water by Adsorption: A Review

“…The ionic strength has the ability to affect the binding of the adsorbed species [1,54] and therefore compete for adsorption sites. By determining the effects of ionic strength, the inner-sphere and outersphere ion-surface complexes can be distinguished [129].…”

“…By determining the effects of ionic strength, the inner-sphere and outersphere ion-surface complexes can be distinguished [129]. Outer-sphere complexes are predictable to be more vulnerable to ionic strength variations than inner-sphere complexes because the background electrolyte ions are positioned in the same plane for outer-sphere complexes [1]; therefore a decrease in the adsorption is observed when conversely the electrolyte concentration is increased due to competition for adsorption sites [130]. Ions that form inner-sphere complexes are straight synchronized to surface groups and may not compete or compete at lower percentage with electrolyte ions [130].…”

“…Adsorption process among several treatment technologies is applied for removal of fluoride (F − ), arsenite (As(III)), and arsenate (As(V)) ions due to the availability of local material and being easy to operate and maintain and in general it is a low-cost technology and is suitable for use in developing countries. The adsorption process is influenced by several environmental conditions, such as pH, salt effect, or ionic strength, the presence of other anions, cations, and organic matter, and adsorbate physical and chemical properties which have been reported in previous studies [1][2][3][4][5]. However, no previous study was done to compare the two anions based on the influence factors such pH, salt effect, or ionic strength and the presence of other anions and their relationship on the adsorption isotherm.…”

Woods Charred at Low Temperatures and Their Modification for the Adsorption of Cr(VI) Ions from Aqueous Solution

“…8.23%, 29.78%, 46.52%, 29.33% and 10.44% for C1, C2, C3, C4 and FLC, respectively. A further increase in the ionic strength from 0.01 to 0.5 M increased the value of % R for all the adsorbents except for C1 and FLC, with the final % R values at I = 0.5 M appearing to be close to those at I = 0.001 M. Adsorbents C1 and FLC exhibited similar behaviours, with the % R values continuously decreasing as the ionic strength increased from 0.01 to 0.1 M, but increasing when the ionic strength was greater than 0.1 M. The adsorption of Cr(VI) ions onto C1 at I = 0.5 M was only 19.2% of the value obtained at I = 0.001 M. In contrast, the adsorption of Cr(VI) ions onto hematite and goethite was strongly dependent on the pH but independent of the ionic strength (Ajouyed et al 2009). However, our results show that the ionic strength had a negative effect on the adsorption of Cr(VI) ions at I < 0.1 M, but became positive at I > 0.1 M.…”

“…Normally, it is difficult to clean up wastewater containing low concentrations of Cr(VI) ions at neutral pH values. Thus, for example, the removal extent of Cr(VI) ions by natural iron oxide (goethite) has been reported to be reported only 40% at pH 6.5 when the initial Cr(VI) ion concentration was 0.1 mg/ᐉ (Ajouyed et al 2009). …”