Release and transform of lead from the glass of cathode ray tube (CRT) following its entrance in the soil

The objective of this study was to investigate the release and transform Pb from the CRT glass following its entrance into the soil environment. A long-term incubation of soil mixed with CRT glass particles and sequential selective dissolution technology were used. Results indicated that the addition of CRT glass particle to the soil led to the increase in the total concentration of Pb in the soil from 28.4 mg/kg to 8 634.4 mg/kg. In details, the concentrations of Pb in the soluble and exchangeable form (EXC-Pb) and bound to the carbonate minerals (CARB-Pb) and manganese and iron oxides (RO-Pb) were 0.20-0.98 mg/kg, 20.1-103.6 mg/kg, and 26.7-54.3 mg/kg, respectively. The sum of these three fractions of Pb was 48.6-155.2 mg/kg. In the EXC, CARB, and RO dissolution steps, the concentrations of Pb directly released from the surface of the CRT glass particles were only (0.038 ± 0.025), (7.55 ± 3.13), (7.55 ± 3.13) mg/kg, respectively. Hence, the released Pb from the CRT glass was mostly bound to the carbonate minerals and manganese and iron oxides in the soil. The decrease of pH from 8.0-8.3 to 7.1-7.5 did not significantly affect the chemical forms of Pb in the soil. The release rates of Pb from the CRT glass to the EXC, CARB, and RO forms were 0.15/t, 21.1/t, and 3.8/t mg·(kg·d)^-1 respectively (t is incubation time in unit of d). The CARB-Pb or RO-Pb might transform to EXC-Pb when pH or Eh of soil decreases, thus entrance of CRT glass particles in the soil environment may pose an ecological risk.