Feasibility study of manganese separation from industrial wastewater by surface absorption method with graphene adsorbent from industrial wastewater

Abstract
The issue of water supply is the most important side service of every industrial unit, which turns into industrial wastewater during various uses, it is important to obtain industrial wastewater recovery methods. In the present study, manganese removal experiments by graphene adsorbent were carried out continuously in different conditions. Then the effect of effective parameters on manganese absorption such as pH (from acidic environment 2 to basic environment 12), contact time (from 5 to 30 minutes), initial concentration 20ppm and amount of adsorbent used (0.02 gr, 0.04 gr, 0.06 gr, 0.08 gr and 0.1 gr) ) was investigated. An atomic absorption device was used to measure the amount of manganese in the solution. The results showed that the optimum playing medium for the adsorbent was equal to 10. In the study of the effect of adsorbent heat on the absorption percentage, it was observed that the nanographene used has an extremely high absorption power in removing pollutants. The results showed that the process of removing manganese from the aqueous solution follows the pseudo-quadratic equation with very high accuracy. The maximum removal of manganese from the aqueous solution was 2ppm by 0.08gr of nanographene in 10 alkaline environment and 30 minutes contact time, and the absorption percentage was 99.05%.Graphene has a very good performance in removing manganese metal from wastewater. In fact, the larger the size of the absorbent surface and pores, the higher the absorption rate.
Introduction
Today, according to the strict laws that have been developed to protect human health and the environment, as well as to compensate for the lack of water resources available to communities, it is necessary to take measures to remove pollutants from the mixture of sewage and polluted water. To be done with high efficiency. While the above methods have low efficiency in removing heavy metals (such as sedimentation methods) or show their best efficiency in concentrated wastewater containing heavy metals (such as ion exchange methods) and solvent extraction) and therefore it is not suitable for removing low concentrations of heavy metals from industrial wastewaters and bringing their quality up to the existing standards, and since heavy metals do not disappear in nature, it is necessary It is up to new technologies to remove them and separate them from the sewage. Considering the importance of applying and introducing up-to-date and efficient methods and the environmental importance of nickel element in industrial effluents, in the present study, the ability and feasibility of removing manganese from industrial effluents based on the adsorption-surface method using graphene is investigated. . Graphene has a high level of porosity, flexibility, stability and electrical conductivity, which are very suitable features for absorbing heavy metals on an industrial scale. In this study, while investigating the effectiveness of graphene in separating nickel from wastewater, the effect of variables such as temperature, pollutant concentration, adsorbent concentration, contact time, and pH on the amount of metal absorption by the adsorbent is investigated.
Methodology
Sampling was done in glass bottles that were previously washed with distilled water. The approximate amount of water collected was around 500 ml, and the date, time and exact place of sampling were noted on the bottles. In the beginning, the experiment was used to study the effect of initial pH, contact time and the amount of 0.1 g of graphene in 50 ml of solution with a concentration of 20 ppm of manganese. To investigate the effect of adsorbent weight of different amounts of graphene from 0.02 to 0.1 g and 50 mL of solution and to investigate the effect of concentration and determination of adsorption isotherms, manganese with concentrations of 0.5 toppm2 was placed in 50 ml Erlens in the shaker. The effect of pH between 2 and 12 was investigated. In order to adjust the pH of the manganese solution, sodium hydroxide and nitric acid - 0.1 mol L and a pH meter ECO10 model made by Hach Germany were used. Finally, the concentration of manganese in the filtered solutions was measured by a VGA device with an absorption spectrometer. Atomic was measured. In the present study, the effect of parameters affecting adsorption such as initial pH, contact time, initial concentration and weight of graphene was studied by conducting several experiments. The results showed that graphene has a very good performance in removing manganese metal from wastewater. In fact, the larger the size of the absorbent surface and pores, the higher the absorption rate.
Conclusion
The results showed that with the increase in pH, the amount of absorption also increases, and graphene has less tendency to absorb manganese in acidic pH, and as the pH increases towards the alkaline environment, the amount of absorption also increases. The pH of the environment is known as the most important effective factor in the absorption process. Because increasing or decreasing the pH of the environment changes the ionic state in metals. These pH changes cause ionization of the adsorbent surface, which affects the adsorption process .By increasing the initial concentration of manganese, its absorption percentage decreases, but the absorption capacity of manganese increases, which is due to the saturation of the absorbent surface. Investigating the effect of contact time on the amount of manganese absorption showed that if the mixing time is increased, they will not have a constant adsorbent efficiency and significant amount of absorption. The obtained results showed that most of the absorption takes place within 30 minutes. In the study of Chobdaran et al., 2015, the separation of manganese from industrial wastewater was investigated using the process of surface absorption by anthracite and its comparison with activated carbon, and the results showed showed that with increasing contact time, the absorption rate increased and absorption reached equilibrium in 70 minutes. With the increase in contact time, the amount of absorption increases due to the increase in the opportunity and chance of metal ions meeting with absorbent particles.
In the study of Saadati and Shoogardzadeh., 2019, which investigated the removal of nickel, the results showed that the equilibrium data of nickel adsorption on silica airgel/active carbon nanocomposite followed pseudo-second-order kinetics. The results of the present study showed that with increasing metal concentration, the removal percentage decreases. This can be attributed to the increase in the ratio of cations in the solution to the absorbent surface. By increasing the amount of adsorbent, the number of available adsorption sites for metal ions increases; Therefore, the efficiency of the absorption process increases, but the absorption capacity decreases, which is because the sites are not saturated in the absorption reactions.
Studies of adsorption isotherms showed that the adsorption process of manganese by graphene is in good agreement with Freundlich, Langmuir and Temkin equations, and Langmuir adsorption isotherm equation has a higher correlation coefficient compared to Freundlich and Temkin equations.
suggestions
1) Carrying out experiments on the absorption of manganese from the solution phase in the adsorbent column (continuous)
2) Investigating the absorption of manganese from the gas phase
3) Investigating the performance of graphene in real environments, by carrying out absorption from other polluted industrial wastes, and also for surface absorption of heavy metals.
4) Examining the experiments at higher concentrations and also studying the synthetic absorption for temperatures of 35 and 45 degrees.
Keywords: graphene, surface adsorption, adsorption isotherm, manganese, wastewater