Heavy Metal Recovery from Waste CRT Funnel Glasses by the Combined Process of Rapid phase-separation and Mechanochemical Extraction

Abstract

An innovative and sustainable method of extracting heavy metal oxides (PbO, BaO, and SrO) from a cathode ray tube (CRT) funnel glass was developed. Funnel glass was first remelted with 20 wt % B2O3 at 1000 °C for 30 min in air atmosphere. Most of the heavy metal oxides (PbO, BaO, and SrO) were quickly migrated from the funnel glass to the B2O3-rich phase. Then, heavy metal oxides were recovered efficiently from phase separation product by a sustainable wet ball-milling process (replaced the traditional strong acid) using ethylene diamine tetraacetic acid (EDTA) as extraction reagent at room temperature. Mechanical activation caused the rapid dissolution of the B2O3-rich phase in water. Thus, heavy metal cations (Pb2+, Ba2+, and Sr2+) could be extracted as a metal-EDTA, and the solid residue was high silica glass powder (silica purity >92 wt %). The extraction rates of Pb, Ba, and Sr were 95.74%, 93.57%, and 94.76% when only milling for 5 min and reached 99.35%, 98.07%, and 96.40% for 60 min under optimum conditions: EDTA adding amount, 2 g; rotational speed, 500 rpm; and water/solid ratio, 0.8, respectively. Heavy metal ions could be recovered by sulfate precipitation, and the soluble metal-EDTA could be transformed into solid EDTA when pH < 3. Thus, this paper provides a sustainable method for detoxification and reutilization of heavy metals containing silicate waste.