Recycling and modeling of chromium from sludge produced from magnetic flocculation treatment of chromium-containing wastewater

In this paper, an effective and sustainable treatment method for recycling chromium from sludge produced by magnetic flocculation was established. Chromium was extracted from sludge with hydrogen peroxide and sodium hypochlorite, and then, superparamagnetic ferroferric oxide nanoparticles (MPs) were recovered by magnetic separation. The recovery percentage of chromium with sodium hypochlorite was higher than that with hydrogen peroxide, and the maximum was 99.12%. With increasing MPs use times, the adsorption percentage of chromium decreased, but there was no significant change in the recovery percentage of chromium in sludge. The purity of the recovered sodium chromate crystals was 96.28%. The back-propagation algorithm was used to model chromium recovery. The correlation coefficient between the model prediction data and experimental data was 0.9990, and the average absolute error was 0.51. The maximum recovery percentage of chromium obtained from model prediction was 99.27%, and the corresponding optimal conditions were consistent with those of experiments. © 2021 Institution of Chemical Engineers