| چکیده انگلیسی مقاله |
IntroductionToxic and dangerous pollution in groundwater is enormous. This assenic pollution is concentrated more thanits permissible limits. It can be observed in different countries like India, Nepa l,Bangladesh, Pakistan, Taiwan,Thailand, Vietnam, Argentina, Brazil, Chili and Mexico. In some places in Iran like Hashtgerd and Kordestanthe arsenic pollution has been observed more than the permissible concentration. As the arsenic pollution isincreasing, many studies have been done to find different treatment options. Due to rapid removing of the As (V)and As (III) by using Iron Nano particles, this method have recently been considered useful.In this paper arsenic removal process was investigated by using nanoparticles. Based on batchexperiments, the influence of Zero-valent iron nanoparticles concentration, tem perature, pH, time, andarsenic initial concentration were observed in arsenic removal process. The results of this studyindicated that the Iron nanoparticles have high performance in arsenic pollution removal.Experimental MethodThe purpose of the current experimental study was to investigate the arsenic remediation process by using ironnanoparticles in batch experiment. Specific concentration of iron nanoparticles produced by PNF Corporationalong with the arsenite sodium salt was used. Specification of iron nanoparticle and arsenic has been shown intable 1 and 2.Table 1. Arsenic proportions in arsenic sodium saltElement Valance Percent % gr/ 1000ppmNa 23 0.18 0.31As 74.9 0.58 1O2 32 0.25 0.43NaAsO2 129.9 1 1.73Table 2. Specifications of iron nanoparticlesActual density(gr/Cm3)Bulk density(gr/Cm3)Specific surface(Cm2/gr)Purity(%)99.9 8-6 0.25-0.1 7.9Firstly, the polluted arsenic solutionw as put on shaker with a speed of around 250 rpm . Thenspecific concentration of iron nanoparticles were added to the solution and the test was begun. Thearsenic reducing process was investigated with sampling, conducted during the experiments. Sampleswere kept in dark glassetos prevent the arsenic oxidation. It should be m entioned that ironnanoparticles were separated from samples by filtering papers S&S with the size of 11m. Arsenicwas measured by coupling VGA and atomic adsorption machineries and the results were finallyanalyzed. In batch experiments, the effect of five parameters, i.e. time, pH, temperature, initial concentrationof arsenic and injection concentration of nanoparticles were investigated. Specifications of theexperiment have been showed in Table 3.Table 3. Specifications of experimentalTime(min)Iron nanoparticlesconcentration (gr/lit)Arsenic initialconcentration (ppm)SpecificationsExperimentalTime 0.5 1 2,5,10,15,30,60,90,120Iron nanoparticles concentration 0.5 0.5, 2 30,60,90,120Arsenic initial concentration 0.5, 5 1, 2 30,60,90,120Temperature 0.5 1 15,30,45,60pH 0.5 1 30,60,90,120In the first test, the solution containing 0.5 gr/lit arsenic and 1 gr/lit nanoparticles reacted after 1hour and the results showed that arsenic concentration reduced to below the allowable concentrationby using Fe nanoparticles in this time interval (Fig. 1 and 2). In pH test, alkaline, acidic and naturalenvironments were investigated and the result indicated that the reaction rate increased withdecreasing of pH. The results also indicated that pH increased during the test (Fig4) and this result wasone reason for decreasing reaction rate with time. For studying the temperature effect, two similar testswere done in 60C and 30C temperatures. In these tests, the reaction rate increased with increasingthe temperature. Initial arsenic concentration and injection iron concentration affected the reaction ratesignificantly. Consequently, the experiments were conducted by considering different concentration ofiron nanoparticles and arsenic thawt ere for arsenic concentration 5 and 0.5 ppm and for ironnanoparticles of 2 and o.5 gr/lit (Table 3). After that, the results indicated that the reaction rateincreased with increasing the arsenic or iron nanoparticles concentration (Fig. 3) because of theincrease in the contact between arsenic pollution and iron nanoparticles as reactive. Finally, the resultsrevealed that iron nanoparticles could effectively been used to eliminate the arsenic pollution. ConclusionNowadays, arsenic remediation as a toxic and widespread pollution is important in groundwater studies. One ofthe methods for the arsenic remediation is using the iron nano particles. This method involves lower costs withhigh performance and can be used for in-site pollutant remediation in aquifers. The result of this investigationindicated that the reaction between iron nanoparticles and arsenic lasts only about several minutes. Increase inthe temperature and decrease in pH reduced the reaction rate. Investigation of arsenic concentration com paredwith iron nanoparticles injection concentration revealed that the arsenic removal rate is increased by an increasein the ratio of nanoparticles to arsenic. For removing 500 ppb of arsenic concentration by using 1 gr/lit of ironnanoparticles, an exponential decreasing process was observed so that the arsenic concentration was reached toless than the arsenic permissible concentration during two hours. Finally it can be concluded that the capabilityof the Zero-valent Fe nanoparticles is a useful tool for removing the arsenic pollution in the groundwater. |