Remediation of Cr (VI) by inorganic-organic clay.

Application of inorganic-organic clays (IOCs) for the remediation of hexavalent chromium (Cr (VI)) and the effect of bisphenol-A (BPA) were investigated. IOCs were better adsorbents for the removal of Cr (VI) than organoclay. Solution pH significantly affected the surface charge of IOCs and speciation of Cr in the solution; hence, the adsorption of Cr onto IOCs. Pseudo-second order model and Langmuir model were the best fit for the kinetics and equilibrium data, indicating chemisorption and formation of monolayer on homogenous adsorption sites, respectively. Cr (VI) adsorption by IOCs was driven by electrostatic interactions between positively charged IOC surfaces and HCrO4- anions. The IOC adsorption capacity for Cr (VI) correlates with the amount of loosely held ODTMA on the external surface of the clay. Involvement of an anion-exchange reaction was suggested in which the counter halide ions of the cationic surfactants were replaced by HCrO4- anions. Cr (VI) adsorption was not affected by the presence of BPA in the medium and two mechanisms for the adsorption of BPA and Cr (VI) were suggested. Partial reduction of Cr (VI) to Cr (III) was observed on the surface of IOC and the reducing agent responsible was suggested to be the Fe (II) in montmorillonite.

A performance evaluation of a new iron oxide-based porous ceramsite (IPC) in biological aerated filters.

A novel medium containing iron oxide-based porous ceramsite (IPC) and commercial ceramsite (CC) was used in two laboratory-scale upflow biological aerated filters (BAFs) to treat city wastewater to compare their efficacy in wastewater treatment. The IPC BAF and CC BAF were operated in water at 20-26°C, an air/water (A/W) ratio of: 3:1 and hydraulic retention times (HRTs) of 7, 3.5, 1.75, and 0.5 h and the removal of ammonia nitrogen (NH3-N), total nitrogen (TN), total organic carbon (TOC), and phosphorus (P) were studied. Our results indicated that IPC BAF was superior to CC BAF in terms of TOC, TN, NH3-N, and P removal. IPC had higher total porosity and larger total surface area than CC. The interconnected porous structure of IPC was suitable to microbial growth, protozoan, and metazoan organisms were primarily found in the accumulated biofilm layer. Biomass, in the biofilm layer, was detected at three distinct distances (300, 900, and 1500 mm) from the bottom of the inlet filter, again indicating that the IPC was more suitable for biomass growth. The presence of biomass improves the simultaneous removal efficiency of nitrogen and phosphorus in the IPC BAF. Thus, our findings support IPC as a material for use in filter media in wastewater treatment BAFs.

Environmental applications of inorganic-organic clays for recalcitrant organic pollutants removal: Bisphenol A.

Bisphenol-A (BPA) adsorption onto inorganic-organic clays (IOCs) was investigated. For this purpose, IOCs synthesised using octadecyltrimethylammonium bromide (ODTMA, organic modifier) and hydroxy aluminium (Al13, inorganic modifier) were used. Three intercalation methods were employed with varying ODTMA concentration in the synthesis of IOCs. Molecular interactions of clay surfaces with ODTMA and Al13 and their arrangements within the interlayers were determined using Fourier transform infrared spectroscopy (FTIR). Surface area and porous structure of IOCs were determined by applying Brunauer, Emmett, and Teller (BET) method to N2 adsorption-desorption isotherms. Surface area decreased upon ODTMA intercalation while it increased with Al13 pillaring. As a result, BET specific surface area of IOCs was considerably higher than those of organoclays. Initial concentration of BPA, contact time and adsorbent dose significantly affected BPA adsorption into IOCs. Pseudo-second order kinetics model is the best fit for BPA adsorption into IOCs. Both Langmuir and Freundlich adsorption isotherms were applicable for BPA adsorption (R(2)>0.91) for IOCs. Langmuir maximum adsorption capacity for IOCs was as high as 109.89mgg(-1) and it was closely related to the loaded ODTMA amount into the clay. Hydrophobic interactions between long alkyl chains of ODTMA and BPA are responsible for BPA adsorption into IOCs.

Structural and thermal properties of inorganic-organic montmorillonite: Implications for their potential environmental applications.

Inorganic-organic clays (IOCs), clays intercalated with both organic cations such as cationic surfactants and inorganic cations such as metal hydroxy polycations have the properties of both organic and pillared clays, and thereby the ability to remove both inorganic and organic contaminants from water simultaneously. In this study, IOCs were synthesised using three different methods with different surfactant concentrations. Octadecyltrimethylammonium bromide (ODTMA) and hydroxy aluminium ([Al13O4(OH)24(H2O)12](7+) or Al13) are used as the organic and inorganic modifiers (intercalation agents). According to the results, the interlayer distance, the surfactant loading amount and the Al/Si ratio of IOCs strictly depend on the intercalation method and the intercalation agent ratio. Interlayers of IOCs synthesised by intercalating ODTMA before Al13 and IOCs synthesised by simultaneous intercalation of ODTMA and Al13 were increased with increasing the ODTMA concentration used in the synthesis procedure and comparatively high loading amounts could be observed in them. In contrast, Al/Si decreased with increasing ODTMA concentration in these two types of IOCs. The results suggest that Al-pillars can be fixed within the interlayers by calcination and any increment in the amount of ODTMA used in the synthesis procedure did not affect the interlayer distance of the IOCs. Overall the study provides valuable insights into the structure and properties of the IOCs and their potential environmental applications.