Synergistic heterogeneous electro-Fenton process using iron-loaded bentonite for binary dyes degradation from wastewater

This study examines the impact of operational parameters on the performance of a heterogeneous electro-Fenton process for removing a binary mixture of malachite green (MG) and methylene blue (MB) using iron-loaded bentonite clay (Fe-Bent.) particles as a heterogeneous catalyst. The effects of current density (j), Fe-Bent.* dosage (Bent. quantity variable) and Fe*-Bent. dosage (iron concentration variable), were investigated. Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray fluorescence and scanning electron microscopy were used to extensively evaluate the synthesized catalyst, confirm­ing the effective incorporation and uniform distribution of iron within the bentonite clay. The results showed that increase of j enhanced dye removal efficiency to over 95 % for MG and 90 % for MB at 20 mA cm-². Furthermore, increasing the dose of Fe-Bent.* from 1 to 3 g improved the overall removal efficiency, although this was accompanied by a decrease in adsorption capacity and a deviation from ideal kinetic behaviour at higher loadings. Fe*-Bent. dosage with a variable iron concentration from (0.1 to 0.2 mM) exhibited the highest removal efficiency, while increasing to 0.3 mM resulted in decreased process performance. The comparison results showed that the electro-Fenton process alone achieved limited removal, whereas bentonite adsorption alone provided high but incomplete removal. In contrast, the heterogeneous electro-Fenton process achieved the highest efficiency (98.06 % for MG and 91.14 % for MB, with COD values of 84.53 % for MG and 79.82 % for MB), with the lowest iron leaching (<0.1 ppm), well below regulatory limits. These results demonstrate the clear advantage of the heterogeneous electro-Fenton process for efficient and environmentally friendly removal of mixed dye pollutants.