Backgrond and Objective: CHROMIUM (III) salts are the most widely used chemicals for tanning processes, but 30-40% of the CHROMIUM amount remains in the solids and liquid wastes )especially spent tanning solutions). Therefore, the removal and recovery of the CHROMIUM content of these wastewaters is necessary for environmental protection and economic reasons. The aim of this study was chromiam removal from tannery wastewater by precipitation process.Materials and Methods: Removal and recovery of CHROMIUM were carried out by using precipitation process. To this purpose, three precipitating agents were used; calcium hydroxide [(Ca(OH)2)], sodium hydroxide (NaOH) and magnesium oxide (MgO). The effects of pH, stirring time, setteling rate and sludge volume were studied in batch experiments.Results: Results showed that the optimum pH was 8-9, and the setteling rate of the process for magnesium oxide was much more than this rate for the other two compounds. Furthermore, a grainy, dense, easly settelable precipitate could also be formed when MgO was used as the precipitator. Whereas, precipitates forming by NaOH was very gelatinous and the setteling rate was low. Precipitates forming by Ca(OH)2 was not also desirable. Sludge's volume by MgO was much less than sludge volume produced by Ca(OH)2 and NaOH.Conclusion: The MgO is an effective and suitable precipitating agent for removal of CHROMIUM from tanning wastewater.

Environmental pollution by various pollutants is one of the most important problems of this century. At least 20 elements, including CHROMIUM have been classified in toxic metals group, that half of them are released in the environment in excessive amounts of standards. CHROMIUM is a toxic pollutant that is widely spread in the environment and exists in cement and concrete. The aim of this study is measurement of CHROMIUM concentrations in samples of surface soil area around and inside the cement plant. 26 random samples were collected and analyzed from the inner yard of cement plant and 29 samples from different directions and radii in the range from 520-3150 m around the plant with considering topography limitations, AC/AQ techniques and sampling size number. Soil samples were prepared for flame AAS analyzing by International Standard method (ISO 11466). The CHROMIUM concentration in soil samples around the plant is 29.06±3.53 mg/kg and inside the plant samples is 42.11±11.08 mg/kg that these values are lower than the standard set for CHROMIUM (100 mg/kg). Contamination levels were estimated based on the Igeo. The indices showed a level of contamination of the metal CHROMIUM is uncontaminated to moderately contaminated. ANOVA test results showed Cr concentration difference between inside and outside the factory was significant (p value = 0.05). This factory in terms of trace element CHROMIUM is not a pollutant.

In this study tribological properties of pulsed electrodeposited crack free CHROMIUM and DC electrodeposited hard CHROMIUM coatings were studied, by using a dray reciprocating pin on plate wear testing machine. The crack free coatings showed higher wear rate and coefficient of friction than the hard coatings. The wear mechanism in these coatings was mainly adhesive, while the mode of the wear in the hard coatings was mainly abrasive.

This study aims to report Batch adsorption study of hexavalent CHROMIUM, Cr (VI) on zeoliteNaX. Kinetics of Cr (VI) adsorption and adsorption isotherms were determined by varying operating parameters such as pH, initial concentration, temperature and contact time. ZeoliteNaX was found to remove Cr (VI) in acidic solutions down to ppm level at pH of about 4. Removal rate of Cr (VI) was found to decrease as pH rises above 4.0. Langmuir, Freundlich, Temkin and Redlich-Peterson models were applied to adsorption equilibrium data to find the best amongst these models. Langmuir model with R2 = 0.9711 best fits the adsorption data. The kinetics of adsorption was found to follow the first order reversible reaction. The separation parameter, RL values of less than 1.0 i.e., 0.7369, 0.5834 and 0.4828 corresponding to initial concentrations of 10, 20 and 30 mg/L, respectively indicated that adsorption of Cr (VI) on zeoliteNaX is favoured. The estimated values of thermodynamic parameters such as heat of adsorption and standard gibbs free energy confirmed the exothermic nature of adsorption of Cr (VI) on zeoliteNaX.

Introduction: In electroplating processes, hexavalent CHROMIUM mist is emitted in air. Hexavalent CHROMIUM mist can cause lung cancer and nasal septum in workers. As Permissible Exposure Limit (PEL) of hexavalent CHROMIUM is low (0.5 mg/m3) and it is used in various industries, evaluation of workers exposure to hexavalent CHROMIUM is very important. However, hexavalent CHROMIUM is relatively unstable and it can be reduced to trivalent CHROMIUM during sampling, storage, and extraction. So, factors influencing determination of Cr (VI) must be evaluated. In this study, influence of some factors such as sampling time, storage time, type of filter, and storage temperature on reduction of Cr (VI) were investigated.Materials and Methods: In this study, based on experimental design, 168 hexavalent CHROMIUM mist samples were collected and analyzed according to the NIOSH 7600 method. All samples were collected by two types of filters (PVC, BQFF) at different sampling durations (30, 180, 480 min) and different storage times (0, 3, 24, 72 hours). Some samples were analyzed immediately after sampling and some of them were stored at 3, 24, and 72 hours at two different temperatures (20-25oC, 4oC).Results: Results showed that, Cr (VI) concentration was decreased with increasing the sampling time (Pvalue<0.001), also, Cr (VI) concentration was decreased gradually with increasing of storage duration (Pvalue< 0.001). Hexavalent CHROMIUM mean concentration in BQFF filter was more than PVC filter (Pvalue<0.001). Also, storage temperatures had no effect on reduction of Cr (VI) (Pvalue>0.05) Conclusion: Because of acidic and instability of Cr (VI) mist air, by increasing sampling time, Cr (VI) is reduced. Also, acidic media of filter at sample storage can cause possible reaction of polymeric and oligomer materials of filter media with Cr (VI), in which, with increasing storage time, Cr (VI) can be reduced on filters. On the whole, at starting sampling times (30 min) BQFF is more efficient than PVC for collection of Cr (VI). Based on the obtained results, storage conditions of samples had no effect on Cr (VI) reduction.

Hexavalent CHROMIUM is a pollutant found in surface and underground waters that causes serious environmental hazards. CHROMIUM enters water as a result of industrial activities such as electroplating, dyeing, leather tanning, and metal manufacturing. The objective of the present laboratory-experimental study was to remove chromate from industrial effluents using silicon nanoparticles. The experiments were performed with both simulated synthetic wastewater and true wastewater. Various parameters such as pH, contact time, and different concentrations of Cr (VI) and SiO2 were examined. The data obtained were analyzed using the Excel and SPSS Ver. 16. It was found that Cr (VI) removal increased with decreasing pH and increasing contact time. The highest Cr (VI) removal was achieved at pH=3 and a contact time of 120 minutes. It was also observed that removal observed to obey the Langmuir isotherm and pseudo second-order kinetic models, respectively. The findings indicate that silicon nanoparticles are capable of removeing Cr (VI) from industrial effluents. Given the Cr (VI) removal efficiency of 93.6% achieved under optimum conditions and the removal efficiency of 88.6% achieved in real samples, the method may be recommended as a highly efficient one for removing Cr (VI) from industrial wastewaters.

In this study, different amounts of MoS2 particles and an anionic surfactant were added to the conventional CHROMIUM electroplating bath in order to electrodeposite crack-free CHROMIUM coatings and the structure, morphology, tribology and corrosion behavior of the deposited coatings were investigated using X-ray diffraction spectroscopy, scanning electron microscopy, pin on disk wear test method, dynamic polarization, and electrochemical impedance spectroscopy techniques, respectively. The results showed that the incorporation of MoS2 particle into the electrodeposited Cr coatings is impossible and no CHROMIUM coating can be electroplated from baths containing more than 5 g/L MoS2 particles. In addition, as the MoS2 concentration in the bath increases up to 1 g/L the corrosion and wear resistance of the deposited coatings increases. Moreover, those coatings that were electroplated from the baths containing more than 1 g/L exhibited less performance regarding their corrosion and wear behavior.