Sodium alginate encapsulated nano zero valent iron loaded in aminated magnesium hydroxide for effective removal of chromium

Abstract

Chromium-containing wastewater is one of the major pollutants affecting water safety. The adsorption-reduction property of nano zero-valent iron particles (nZVI) is an effective way to counter chromium pollution. However, nZVI is affected by surface passivation as well as agglomeration in the process of use. To overcome this limitation and to strengthen its performance in the treatment of chromium-containing wastewater, we proposed a new approach by sodium alginate (SA) encapsulated nZVI loaded in the pores of aminated spherical magnesium hydroxide (MH-NH2). The prepared ternary composite (nZVI@SA/MH-NH2) exhibited better stability, dispersibility, larger specific surface area, and more active sites. We found that nZVI@SA/MH-NH2–1 could remove 97.92% of Cr(VI) from the solution within 5 min at pH = 3 without oxygen. Adsorption capacity of nZVI@SA/MH-NH2–1 could reach 134.00 mg/g. Moreover, the acidic environment could achieve the slow release of OH− at the expense of MH-NH2 carriers to increase the pH of the solution, enabling the generated Cr(III) to form Cr(OH)3 and precipitate out of the solution. nZVI@SA/MH-NH2 could achieve the removal of total chromium from the solution in one step. This strategy contributed to the cheap and efficient separation of Cr(VI) together with Cr(III) from the wastewater.