Effect of Humic Acid on the Removal of Chromium(VI) and the Production of Solids in Iron Electrocoagulation

Abstract

Iron-based electrocoagulation can be highly effective for Cr(VI) removal from water supplies. However, the presence of humic acid (HA) inhibited the rate of Cr(VI) removal in electrocoagulation, with the greatest decreases in Cr(VI) removal rate at higher pH. This inhibition was probably due to the formation of Fe(II) complexes with HA that are more rapidly oxidized than uncomplexed Fe(II) by dissolved oxygen, making less Fe(II) available for reduction of Cr(VI). Close association of Fe(III), Cr(III), and HA in the solid products formed during electrocoagulation influenced the fate of both Cr(III) and HA. At pH 8, the solid products were colloids (1-200 nm) with Cr(III) and HA concentrations in the filtered fraction being quite high, while at pH 6 these concentrations were low due to aggregation of small particles. X-ray diffraction and X-ray absorption fine structure spectroscopy indicated that the iron oxides produced were a mixture of lepidocrocite and ferrihydrite, with the proportion of ferrihydrite increasing in the presence of HA. Cr(VI) was completely reduced to Cr(III) in electrocoagulation, and the coordination environment of the Cr(III) in the solids was similar regardless of the humic acid loading, pH, and dissolved oxygen level.

Adsorption mechanism of Cr(VI) onto GO/PAMAMs composites

“…Various methods have been investigated to remove Cr(VI) from industrial wastewater, such as electro-coagulation 7 , photo-catalytic reduction 8,9 , membrane separation 10,11 , adsorption 12–14 , ion-exchange 15,16 and microbial remediation 17,18 . Among these methods, adsorption has won a great deal of concern due to it’s a series of advantages, such as cost-effective, high sorption capacity, simple operation and no secondary pollution.…”

Nanoarchitectured Porous Conducting Polymers: From Controlled Synthesis to Advanced Applications

“…[ 83 ] The porous nature of PANI increased the accessibility of NH groups in PANI for the Cr(VI) reduction, while the high H + storage capacity of PANI played an important role in the reduction of Cr(VI). [ 130 ] Bacteria‐templated PANI showed a high Cr(VI) removal rate of 0.5 mg (min g −1 ) with a capacity of 835.06 mg g −1 . [ 83 ] More than 90% Cr(VI) could be reduced to Cr(III) in both neutral and acidic solutions.…”

Formation, aggregation, and transport of NOM–Cr(iii) colloids in aquatic environments

“…11,12 Cr(III) can intimately bind with functional groups of NOM as a monomeric or a polynuclear NOM-Cr(III) complex, 12 which dominates the solubility and mobility of Cr(III) depending on the solution pH. 13 Mounting field-based studies have reported elevated concentrations of organically complexed Cr(III) that remains soluble in natural waters for extended periods of time under neutral pH conditions. [14][15][16] Evidence from laboratory studies further revealed that organically complexed Cr(III) constitutes the main products of Cr(VI) biotic/abiotic reduction under organic-rich conditions.…”