Application of Iron, Aluminum and Copper Composites to Remove High Concentration of Chromium in Water

The increase of various industries and the ever-increasing growth of the population of the planet have caused all kinds of contamination in the environment. One of the most important contaminants in water, which has many risks for human health and living organisms and important environmental risks, is anionic compounds in high concentration. Chromium is one of these contaminants that causes contamination in the environment and brings many risks to human health and other living organisms. Various methods have been evaluated to remove heavy metals from water, which often include chemical or energy-intensive processes. Therefore, it is important to modify these sources with the help of affordable adsorbents and with low energy consumption. Previous studies showed that biochar, metal-coated biochars and carbon-metal composites are highly effective in removing chromium contaminants with a concentration of 20 mg/liter from water, but so far the effect of these adsorbents on removing this anionic contaminant in high concentrations has not been investigated.

In this research, the efficiency of different adsorbents (biochar, copper-coated biochar, aluminum-coated biochar, iron-coated biochar, biochar-copper composite, biochar-aluminum composite and biochar-iron composite) on the removal of chromium, with a concentration of 300 mg per liter, from water was investigated. Metal-coated biochars were prepared from the combination of metals (copper, iron and aluminum) with a concentration of 10000 mg/kg with biochar produced at 600 degrees Celsius and various biochar-metal composites were prepared from the combination of these metals with rice straw and then the samples were pyrolyzed at 600 degrees Celsius. In order to determine the efficiency of the adsorbents, 0.5 grams of each adsorbent was mixed with 40 ml of chromium solution with a concentration of 300 mg/l and pH= 6 and shaken for three hours until they reached equilibrium. Then the samples were centrifuged for 5 minutes at 6000 rpm and after the filtration, the final concentration of the contaminant was obtained and the percentage of chromium removal was calculated.

The results of the present study showed that all of the applied adsorbents were effective in removing high concentrations of chromium from water. The lowest removal rate of this contaminant was related to the biochar sample, which only removed 15.28% of this contaminant from water; And the highest amount of removal was achieved using iron composite, which removed 44.45% of the contaminant from the aqueous solution. According to the results of this research, it can be observed that coating biochar and rice straw with metals has been able to increase the efficiency of this adsorbent in removing chromium from water. For example, iron composite and iron-coated biochar were able to remove 44.45 and 30.86% of chromium contaminant from the aqueous solution, respectively, while rice straw biochar was only able to remove 15.28% of this contaminant from water.

The results of present study showed that iron coated biochar and biochar-iron composite had more ability to remove chromium contaminant from aqueous solution than other metal coated biochars and biochar-metal composites and were able to perform more successfully. Therefore, the use of these adsorbents can be effective in the treatment of chromium-contaminated water.