خالد بن محمد بن ناصر العتيبي

The effect of increasing concentrations of the organic chelating agents EDTA, DTPA and Citrate ( at concentration ranging from 0.005 M and 0.1 M ) on the solubility of Nickel in 95% saturated calcium hydroxide solutions have been investigated as well as the possibility of the formation of Multi-Metal ligand complexes [Ca-Ni-Ligand] by study the effects of increasing concentrations of the calcium hydroxide on the solubility of Nickel in presence of fixed concentrations of the organic ligands in saturated sodium hydroxide . The experiments were carried out in isolated N2 atmosphere in a glove box at a high pH. results show that in increasing concentrations of the organic ligands saturated with 95% Calcium hydroxide, The solubility of Ni (II) increased as the concentration of the organic ligand increased. In increasing concentrations of calcium hydroxide and a fixed concentration of the organic ligands, the solubility of Ni (II) was slightly affected when EDTA and DTPA were present, whereas in the presence of citrate the solubility was highly affected due to the change in calcium concentration, and there was a rapid increase in the solubility of Ni (II) . When the concentration of calcium hydroxide was increased in saturated sodium hydroxide without the present of the organic ligands, the solubility decreased.

Adsorbents were synthesized to obtain novel silica nanoparticles with a broad pore-size distribution (herein referred to as USG-41). The material demonstrated fast adsorption rates with highest adsorption capacities following Langmuir adsorption. Kinetic data best fit the intraparticle diffusion model demon- strating a two-step, surface and pore, adsorption process with pore diffusion being the rate determining step. This data provides key evidence of internal pore chelation of dichromate ions by USG-41. In contrast silica adsorbents (SBA-15 and MCM-41) prepared with similar average pore sizes to USG-41, but with narrow pore-size distributions, had lower adsorption capacities and their kinetic date best fit pseudo-sec- ond order diffusion models indicating a one-step, surface only, adsorption process. This study clearly demonstrated that pores size distribution, not the surface area or the average pore size, was central to ensure optimum adsorbent performance for removal of Cr (VI) from contaminated water.