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a b s t r a c tSulfur compounds exist in the wastewater of industries like paper-making, food processing, photography, etc. Higher levels of sulfate in drinking water lead to its bitter taste and digestive problems as well as corrosion of sewer pipes in addition to causing problems in the anaerobic wastewater treatment processes. Based on this, the present study investigates the equilibrium, kinetics, thermodynamics and isotherms of sulfate removal process by graphene and graphite nanoparticles. This study explored the effects of the parameters including pH, adsorbent dosage, and initial concentration of sulfate, as well as the impacts of contact time and temperature on sulfate removal process in a batch system. The isotherms, thermodynamics and kinetics of the process were also studied. In this study, UV/VIS Spectrometer T80 was used to measure the sulfate concentration. The results obtained from the investigation of the efficiency of graphite and graphene nanoparticles demonstrated that these nanoparticles had the highest adsorption capacity at the acidic pH = 3, adsorbent dose of 0.2 g L -1 and sulfate concentration of 75 mg L -1 . The process of adsorption in graphene and graphite nanoparticles was found to follow the Freundlich isotherm model and pseudo-second-order kinetic model. The results also revealed that sulfate adsorption process with the studied nanoparticles was endothermic. Compared with graphene nanoparticles, the results indicate that graphite nanoparticles have more efficiency in removal of sulfate from aqueous solution. Moreover, the highest removal efficiency by graphene and graphite nanoparticles occurs in higher concentrations of sulfate. Therefore, the two nanoadsorbents can be used in adsorbing sulfate from the aqueous solutions.

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Background: Adsorption isotherms describe the relationship between the equilibrium concentration of the adsorbed matter in the solution and the amount of adsorbed matter on the surface of the adsorbent. Objectives:The main objective of the present research was to investigate different adsorption isotherms for describing adsorption of humic acid by nanoclay. Methods:In this study, Langmuir, Freundlich, BET, Temkin and Dubinin Radushkevich isotherms, for describing the behavior of humic acid adsorption by bentonite and montmorillonite nanoparticles, were examined. Results:The results showed that due to the regression coefficient (R 2 ), humic acid adsorption on bentonite and montmorillonite nanoparticles has greater compliance with Dubinin Radushkevich isotherms. The value of E or average energy of adsorption for humic acid by bentonite and montmorillonite nanoparticles was 0.17 and 0.15 kJ mol -1 , respectively, which specifies that the type of adsorption of humic acid on both nanoparticles was physisorption. The qmax value obtained from the Dubinin-Radushkevich isotherms, for bentonite and montmorillonite nanoparticles were 27.78 and 28.70 mg/g, respectively.Conclusions: According to the results of this study, bentonite and montmorillonite nanoparticles have a great potential for the removal of humic acid from aqueous solutions.

a b s t r a c tThe presence of humic acid, as one of the precursors of trihalomethanes, in water resources causes many health problems for many communities. The purpose of the present study was to investigate the feasibility of ultrasonic process on regeneration of graphene nanoparticles saturated with humic acid. This experimental study was performed in batch condition, which the effects of main parameters such as regeneration time, pH, number of saturation cycles and frequency were investigated for the regeneration of the saturated adsorbent. In the regeneration of graphene nanoparticles saturated with humic acid, the maximum regeneration efficiency, at pH of 11 and regeneration time of 60 min, was 85.37% and 72.47% for frequencies of 60 and 37 kHz, respectively. Regeneration increased with increasing ultrasonic irradiation time. Moreover, the efficiency of regeneration was higher in frequency of 60 kHz compared with frequency of 37 kHz. Adsorption capacity of graphene nanoparticles after five cycles of saturation-regeneration at frequencies of 37 and 60 kHz decreased from 22.65 mg/g to 11.87 and 13.27 mg/g, respectively. The results of regeneration of graphene nanoparticles with ultrasonic waves at frequencies of 37 and 60 kHz showed that the process has a very high efficiency in the regeneration of graphene nanoparticles saturated with humic acid. The process can also be a promising alternative to chemical and thermal regeneration methods.

We aimed to conduct an exposure assessment to dust and free silica for workers of Sangan iron ore mine in Khaf, Iran. The maximum concentrations of total dust and free silica were measured in crusher machine station at 801 ± 155 and 26 ± 7 mg/m(3), respectively. Meanwhile, the minimum concentrations were measured in official and safeguarding station at 8.3 ± 2 and 0.012 ± 0.002 mg/m(3), respectively. Also, the maximum concentrations of respirable dust and free silica were measured in Tappeh Ghermez drilling no. 1 at 66 ± 13 and 1.5 ± 0.4 mg/m(3), respectively, while the minimum concentrations were measured in pneumatic hammer at 5.26 ± 3 and 0.01 ± 0.005 mg/m(3), respectively. Considerate to Iranian standard for respirable dust concentrations (0.11 mg/m(3)) and international standards (ACGIH = 0.1 and NIOSH = 0.05 mg/m(3)), it was found that dust and free silica amounts were much higher than national and international standard levels in this mine.