Removal Of Lead From Waste Cathode Ray Tube Funnel Glass Based On Integration Of Zerovalent Iron With The Ball-milling Process

Among the various kinds of e-waste,waste cathode ray tube?CRT?is the most numerous andhazardous.Almost one-third of the weight of CRT is funnel glass which contains considerable quantities?20%-25%?of toxic lead oxides.It is extremely difficult to extract lead atoms in the funnel glass by using conventional acid leaching methods as they are fixed in the holes of the glass network structure.Consequently,Zero-valent iron has showed an excellent effect on the removal of lead,meanwhile,the application of the mechanical ball-milling has played an important role on dispersing the materials into nano-particles through high-speed strike,so the combination of Zero-valent iron and ball-milling treatment provided a novel and effective system to fully recycle CRT funnel glass.In this study,the removal ratio was studied with these two technologies,the influences of various factors including speed and time of ball milling,particle size and dosage of zero-valent iron,type of nano-iron material were studied,at the same time,the composite material obtained in this progress was characterized and analyzed by XRD,XPS,SEM,XRF,BET,FTIR.Pb,Fe and sodium salts were recovered in the following period.Zeolite was synthesized from the silicon-rich and lead-free liquid with the addition of Al source during hydrothermal treatment.In addition,in order to further explore the way of recycling funnel glass,the microwave extraction was also utilized,the funnel glass was transformed into silicon-rich supernatant for the synthesis of zeolite.The main findings were as follows:?1?The proposed recycling system for waste funnel glass can satisfy the technical and operating-cost merits for large-scale application.The constant amount of lead in funnel glass was 197.35±0.34 mg/g,with the same leaching conditions,the original leaching percentage of lead in acid was 7.11%,and it increased to the maximum percentage of 36.25%after ball milling for 8-96 h.The state change of lead in funnel glass was investigated by the FESEM-EDS,SEP,FTIR,and XPS analyses.The characterization results demonstrated that,with the ball-milling process,the zero-valent iron can permeate into funnel glass network and then destroy the Si–O bonds.Meanwhile,lead gradually transferred from stable residual fraction to unstable exchangeable,carbonate,and Fe-Mn oxide fractions,which greatly enhanced the lead mobility,thereby promoting its extraction efficiency.When the zero-valent iron dosage was 0.5 g/g?zero-valent iron/funnel glass?,the ball-milling time and speed was 72h,375 r/min,the best removal ratio of lead achieved 97.76%.?2?In the recovery stage,lead,iron,and sodium salt from the acid leachate can be recovered as lead sulfate,iron hydroxide,and sodium nitrate through sulfation,alkali neutralization and salt evaporation.The XRD and SEM results showed that the recovered products with higher purity were recovered after treatment.Furthermore,lead,NO₃^-and SO₄^2-concentrations of the resulting drainage were considerably lower than the relevant standard for surface water quality.In additional,the short-term?TCLP?and long-term?MEP?leaching toxicity result of high-silica residue is thought to be safe and reliable to the surrounding environment.?3?In the test of zeolite synthesis from high-silica residue using alkaline fusion method,the crystallization time often interacts with the crystallization temperature in the formation of zeolite molecular sieves.Among that,NaA zeolite completed the growth of zeolite in a shorter crystallization time due to its simple four-membered ring structure.However,as the crystallization time increased,the crystal shape of the zeolite changed from one type to another.High-crystalline zeolites with high CEC value was synthesized from high-silica residue when the silica-alumina ratio is 2:1,the crystallization time was 5 h,and the crystallization temperature was 110°C.?4?In the process of synthesizing zeolite with microwave from waste cathode ray tube funnel glass,the better leaching amount of SiO₂ reached 88.17%with the interaction of hydrofluoric acid and microwave,then regard it as a source of silicon applying to zeolite synthesis using water-soluble method,the results showed that:the too low alkalinity was not conducive to the synthesis of zeolite.When the pH of extract liquor was 13,with the increase of Si/Al ratio,the crystal shape of zeolite was transformed to NaX zeolite from the high purity NaA zeolite,and crystal forms were diverse.And due to the effect of weak acid of HF,the concentration of Pb in the extract liquor was at a lower level,then the lower leaching toxicity of synthetic zeolite was attained.