Effect of Magnetite Nanoparticles and Some Iron-Containing Compounds on the Availability of Arsenic, Iron, Zinc and Copper in Soil

High concentrations of As in contaminated soils represent a potential risk for groundwater sources and threat the food chain. It has been found that the iron-containing compounds used in remediation of As contaminated soils have distinct effects on the solubility of As and can be used as adsorbents for As removal from aqueous and soil solutions. The objectives of this study were to determine As stabilization in soil, with iron-containing compounds and also to compare the fixation of magnetite nanoparticles, ferrous sulfate, ferrosilicon, magnesium ferrosilicon and iron oxide in fixation of arsenic in contaminated soils.

A factorial experiment was conducted using a completely randomized design with three replications. The experimental factors were the amendment types and levels. The modifiers used were magnetite nanoparticles, ferrous sulfate, ferrosilicon, magnesium ferrosilicon, Sfordi, and Golgohar iron soil containing 0, 0.1, 0.2 and 0.3% iron. The soil was artificially contaminated with As (20 mg/kg) using Na2HAsO4.7H2O salt and incubated for 1 month. At the end of incubation time, the modifiers were added to the As contaminated soils and after 3 months, the available fractions of arsenic, iron, zinc and copper were extracted using 0.1 M HCl and measured with ICP.

The results showed that the type and the amount of the modifiers had a significant effect on the available fraction of arsenic and iron in soil (extractable fraction with 0.1 M hydrochloric acid). The available fraction was reduced due to the addition of all  modifiers: Magnetite nanoparticles > iron sulfate > magnesium ferrosilicon > ferrosilicon > Esfordi iron soil and Golgohar iron soil, respectively. The highest decrease in the concentration of available arsenic occurred in the soils treated with 0.3% of modifier. Application of 0.3% levels of magnetite nanoparticles, iron sulfate, ferrosilicon, ferrosilicon magnesium, Golgohar iron soil and Esfordi iron soil stabilized 91, 63, 57, 32 and 48% of arsenic extractable with 0.1 M HCl, respectively. Application of 0.3% of magnetite nanoparticles reduced available arsenic more than other adsorbents. Among the studied  modifiers, magnetite nanoparticles showed more efficiency in chemical stabilization of arsenic in soil. The application of magnetite nanoparticles increased the Fe available fraction in soil. Golgohar iron soil, ferrosilicon, Esfordi iron soil, magnesium ferrosilicon, ferrous sulfate and Magnetite nanoparticles, increased the iron extractable with 0.1 M HCl of the soil, respectively. The highest Fe concentrations were observed in 0.3% of Gol Gohar soil, ferrosilicon, Esfordi soil and ferrosilicon. Increasing the modifiers decreased soil copper extractable with 0.1 M hydrochloric acid concentration and increased soil zinc extractable with 0.1 M hydrochloric acid concentration, which was not statistically significant.

Application of magnetite nanoparticles reduced arsenic concentration more than other adsorbents and showed more efficiency in chemical stabilization of soil arsenic. Other modifiers have also been able to stabilize the arsenic in the soil, suggesting the possibility of using iron-containing modifiers in arsenic-contaminated soils. The use of modifiers increased the iron concentration in the soil. Due to their reasonable price and availability, iron sulfate and magnesium ferrosilicon are recommended for soil arsenic stabilization. At 0.3% soil level, Gol Gohar and Esfordi iron soil were able to reduce 32% and 48% the arsenic concentration, respectively and are recommended for arsenic stabilization in contaminated soil. Golgohar, ferrosilicon, Esfordi and magnesium iron soils caused the highest increase in soil iron concentration. Due to the concentration of other soil elements and the price of modifiers, the level of 0.2% of iron sulfate, Gol Gohar and Esfordi iron soil, ferrosilicon and magnesium ferrosilicon is recommended for stabilization of arsenic in contaminated soil.