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Metal ions such as Cu, Cd, and Zn are toxic and considered as hazardous pollutants due to their stability in the environment. In this study, the natural and Fe (III) modified sepiolite, palygorskite, and zeolite clay minerals were used for the removal of Cu, Zn, and Cd ions from aqueous solutions. The iron chloride 1 M was used for mineral modification and the capacity of sorbent was assessed in a batch experiment containing six starting concentration of sorbents ranging from 10 mg L to 140 mg L. Results of the study showed higher removal efficiency for modified compared to natural clays. Removal efficiency of Cd, Cu, and Zn for zeolite was increased by 15.5, 30.2 and 21.4%, respectively, after modification. Zn removal by sepiolite remained unchanged after surface modification, whereas Cu and Cd removal was increased respectively by 13.6 and 21.2%. Palygorskite modification process also increased 38.14% of Cu, 25.5% of Zn, and 28.4% of Cd sorption compared to its unmodified form. Equilibrium sorption isotherm studies showed that the experimental data were better fitted by the Freundlich sorption isotherm (r > 0.99) than the Langmuir (r > 0.82). In general, the investigated minerals are suggested as efficient sorbents for the removal of Cd, Cu, and Zn ions from contaminated aqueous solutions.

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The role of some humic substances (HS) on phosphorus (P) bioavailability and fractions was investigated in a greenhouse study using a calcareous soil from Eastern, Iran. Soils were treated with two levels (2 and 4%) of Humic Acid (HA), Fulvic acid (FA), Vermicompost (Verm) and their mixtures including FA+HA and FA+HA+Verm, and incubated for 24, 360, 720 and 1080 h. The Olsen-P was determined in amended and nonamended soils after incubation time. The P release was modeled by Parabolic, Power and Elovich equations to determine the transformation rates. Since the maximum P release was found in vermicompost treated soil, P was sequentially extracted with H 2 O, NaHCO 3 , NaOH and HCl at 24 and 1080h after incubation. The highest released P was measured in vermicompost treatment and decreased as follows: HA+FA+Verm>HA+FA>HA>FA>CO. The decrease of P release data was best described by Parabolic equation (r 2 =0.83-0.93, SE=0.51-2.91). Higher transformation indices of vermicomopost amended soil than other treatments showed more efficiency of vermicompost to release of phosphorus in soil. H 2 O-P, NaHCO 3-P and NaOH-P increased after vermicompost application and converted to HCl-P fraction so that at the end of the experiment, calcium phosphates comprised 69 and 43% of inorganic P (Pi) at 2 and 4% vermicomopost treatments, respectively. Results of the study showed that humic substances could increase P extractability and availability in soil.