Reduction of Cr(VI) to Cr(III) and removal of total chromium from wastewater using scrap iron in the form of zerovalent iron(ZVI): Batch and column studies

Abstract

This work experimentally investigates Cr(VI) reduction to Cr(III) using waste scrap iron in the form of zerovalent iron (ZVI) collected from the mechanical workshop of the Institute, both in batch and continuous operation. The reduction of Cr(VI) to Cr(III) was found to be complete (∼100%) depending on the experimental conditions. Lower pH values favour Cr(VI) reduction. Two concurrent reactions take place, that is reduction of Cr(VI) by Fe 0 (ZVI) and by Fe 2+ generated due to H + corrosion of iron. Maximum around 22%, 11% and 2% Cr(III) remained dissolved in solution while the experiments were carried out at initial pH of 2, 4.67 and 7. Higher ZVI loading increases Cr(VI) reduction rate, however, consumption of iron is noted to be higher. The results indicate that the bed is exhausted rapidly at higher pH, initial Cr(VI) concentration and flow rate. This is attributable to predominance passivation of ZVI surface forming Cr(III)-Fe(III)-oxide layer. SEM analysis of ZVI before and after the experiments confirms formation of passive oxide on iron surface is responsible for deterioration of Cr(VI) reduction efficiency due to its blanketing effect.

Removal of Cr(VI) using iron nanoparticles supported on porous cation-exchange resin

“…For 2.7% iron nanoparticles into the support material, the reduction capacity was 28.1 μmol/g that was increased to 32.3 μmol/g when 7.2% iron nanoparticles was used. This trend is similar to the previously reported results of Cr(VI) reduction by iron nanoparticles where higher rates of reduction are associated with higher surface area of contact with the reacting molecule (Parasad et al, 2011). The newly generated Cr(III) and Fe(III) ions as a result of Cr(VI) reduction by iron nanoparticles were captured by the cationic polymer support material.…”

“…It means that with the increase of temperature, the reduction capacity of Cr(VI) to Cr(III) increases. It can be explained by improved reaction rates at higher temperature as described in the literature (Parasad et al, 2011;Shi et al, 2011a,b). The absorption capacity for Cr(III) and Fe(III) were higher at high temperatures.…”

“…The reduction of Cr(VI) to Cr(III) by dispersed iron nanoparticles over the different range of particle diameter of cationic polymer support was observed as 1.2-45 μm N 45-150 μm N 150-270 μm. The reduction of chromium with iron metal was categorized as a simple and efficient mode of reduction according to the following stoichiometric reaction (Parasad et al, 2011):…”

Inorganic engineered nanoparticles in drinking water treatment: a critical review

“…The goal of this process is the reduction of residual concentration below the regulation limit set by international organizations. 61,62 In general, the high reactivity of ZVI nanoparticles explains the improvement of efficiency and kinetics in Cr(VI) removal compared to granular ZVI 63,64 though specific interferences may play an important role. For instance, the regulation limit for arsenic in E.U.…”

Complete Reduction of Hazardous Cr(VI) in Chromium Ore Processing Residue Dump Site

“…In precipitation method, the removal of Cr(VI) is carried out by reducing Cr(VI) to Cr(III) at lower pH range and precipitation of Cr(III) at higher pH value [23]. To 1000 mL of simulated chromium water 0.40 g of Na2S2O4 is added with continuous stirring and the pH of the solution is brought to 2, 2.5 and 3 using pure 1 N H2SO4.…”