This paper assesses the use of certified Iraqi montmorillonite clay as a potential sorbent for the removal of oxytetracycline (OTC) from aqueous solutions. The clay is characterized by a cation exchange capacity of 0.756 meq.g-1 and a zero point charge at pH 8.7. Aqueous solutions of OTC were equilibrated with montmorillonite under various experimental conditions, such as OTC concentration, pH and clay content, for 24 h at fixed ionic strength. Two forms of montmorillonite were evaluated: regular, and iron-modified form. The effect of pH was minor on OTC adSORPTION. Kinetic study revealed that the SORPTION follows a pseudo second order model. SORPTION isotherm showed a good fit with the Fruendlich model. OTC SORPTION onto Fe-saturated montmorillonite was analyzed statistically using a response surface design to study the effects of experimental conditions. The introduction of iron improved the adSORPTION characteristics of the clay due to the ability of ferric ions to make stable complexes with OTC. The most favorable operating conditions for the treatment were deemed as follows: clay content, 6.85 g.L-1, oxytetracycline concentration, 1.0 mmol.L-1 and pH, 5.5 for the iron modified form.

In this paper a chemical method applied to synthesize exfoliated graphite (EG) is presented. In this method graphite intercalation compound (GIC) was firstly synthesized by chemical treatment of graphite flakes using a mixture of sulfuric and nitric acids followed by thermal shock of GIC at 1000°C to produce EG. The bulk density of synthesized EG was found to be as low as 4.5 kg/m3. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for identification and characterization of different materials. According to the XRD observations, the GIC was identified as graphite bisulfate with stage 2, and residue GIC and EG had nearly the same diffraction pattern, but with distinctly lower intensity. In accordance with SEM results the residue graphite bisulfate was swelled in comparison with the graphite flake. The oil SORPTION capacity of synthesized EG in this work was studied by common static and dynamic tests and compared with other sorbents. The results show the superior capability of EG for oil spill cleanup.

Iron oxide nanoparticles (nano-Fe) have been widely used in environmental remediation, including that of emerging contaminants, such as antibiotics. Magnetite nanoparticles (nano-Fe3O4) have been reported to form on the outer surface of nano-Fe and have the potential to be a good sorbent for certain antibiotics. This study reports, for the first time, the kinetics and thermodynamics of adSORPTION of a common tetracycline group antibiotic, oxytetracycline (OTC), on nano-Fe3O4. Batch SORPTION kinetics were evaluated by varying initial OTC concentration (0.25-2 mM), nano-Fe3O4 concentration (2.5-20 g L-1), pH (3.8-7.6), temperature (5, 15, 35 oC), and ionic strength (0.01-0.5 M KCl) to derive thermodynamic and kinetic constants. Results show that OTC SORPTION kinetics is rapid and increases with increasing temperature. The derived thermodynamic constants suggest a surface chemical-controlled reaction that proceeds via an associative mechanism. Results indicate the potential of developing a nano-magnetite-based remediation system for tetracycline group of antibiotics.

Soil adsorbing properties reduce SORPTION ability of the metal, which in turn may influence decision for remediation at contaminated sites. The objective of this study is presentation of a model based on soil properties to estimate the SORPTION of Cr(III) in chromium contaminated soils. Twenty uncontaminated soil samples, with properties similar to the contaminated soils were selected from around of city of Tabriz and treated with Cr as CrCl3. A multiple regression analysis with statgraph software was used to drive an expression that related Cr SORPTION to common soil properties. The results showed that four soil properties were important in determining the amount of Cr adsorbed by the soils including pH, cation exchange capacity, total inorganic carbon and clay content with nearly 80% variability in Cr SORPTION and a reasonable level of confidence by this model. The obtained model suggested that Cr(III) SORPTION was enhanced by higher soil pH, more total inorganic carbon, more clay, and higher cation exchange capacity.

In this work, the effectiveness of native and chemically modified rice bran to remove heavy metal Pb (II) ions from aqueous solution was examined. Chemical modifications with some simple and low-cost chemicals resulted in enhancement of the adSORPTION capacities and had faster kinetics than native rice bran. Experiments were conducted in shake flasks to monitor the upshot of parameters over a range of pH, initial Pb (II) concentrations and contact times using a batch model study. The SORPTION capacities q (mg g-1) increased in the following order: NaOH (147.78), Ca (OH) 2 (139.08), Al (OH) 3 (127.24), esterification (124.28), NaHCO3 (118.08), methylation (118.88), Na2CO3 (117.12) and native (80.24). The utmost uptake capacity q (mg g-1) was shown by NaOH-pretreated rice bran. The results showed that, using NaOH-modified rice bran, the chief removal of Pb (II) was 74.54% at pH 5, primary Pb (II) concentration 100 mg L-1 and contact time 240 min. Equilibrium isotherms for the Pb (II) adSORPTION were analyzed by Langmuir and Freundlich isotherm models. The Langmuir isotherm model, showing Pb (II) SORPTION as accessible through the high value of the correlation coefficient (R 2=0.993), showed a q max value of 416.61 mg g-1. The kinetic model illustrated adSORPTION rates well, depicted by a second order, which gives an indication concerning the rate-limiting step. Thermodynamic evaluation of the metal ion ∆G o was carried out and led to the observation that the adSORPTION reaction is spontaneous and endothermic in nature. NaOH chemically modified rice bran was a superb biosorbent for exclusion of Pb (II) and proved to be excellent for industrial applications.