Coating zirconium oxide-nanocomposite with humic acid for recovery of mercury and chromium in hazardous waste of chemical oxygen demand test

Hazardous waste of chemical oxygen demand (COD) test (HWCOD) is one of the most common laboratory wastewaters,containing large amounts of H_(2)SO_(4)and highly toxic Cr^(3+)and Hg^(2+).Current treatment methods suffered from incomplete removal of Cr^(3+)and high-cost.Herein,a humic acid-coated zirconium oxide-resin nanocomposite (HA-HZO-201) was fabricated for efficient recovery of Cr^(3+)and Hg^(2+)in HWCOD.The synthesized HA-HZO-201 shows excellent tolerance to wide p H range (1–5) and high salinity (3.5 mol/L Na Cl),as well as adsorption capacity for Cr^(3+)(37.5 mg/g) and Hg^(2+)(121.3 mg/g).After treating with HA-HZO-201 by using a fixed-bed adsorption procedure,the final Cr^(3+)and Hg^(2+)concentrations in HWCOD decreased to 0.28 and 0.02 mg/L,respectively.In addition,the HA-HZO-201 can be regenerated by desorption and recovery of Cr^(3+)and Hg^(2+)using HNO_(3)and thiourea as eluents,respectively.After 5 cycles of adsorption/desorption,the removal efficiencies still reach up to86.0%for Cr^(3+)and 89.7%for Hg^(2+),indicating an excellent regeneration of HA-HZO-201.We hope this work open new opportunities for treatment of HWCODwith high-efficiency and low-cost.