Process of Treating End-of-Life Cathode Ray Tubes for Lead and Soluble Silicates Recovery

Abstract

There is described a process of recycling screen glass resulting from the disposal of cathode tube televisions, with quantitative recovery of lead in the form of sulphide and of silicates of cations other than lead, and subsequently recycling all the materials so recovered.

1 . A process of recovering lead and silicates from glasses resulting from cathode tube screen disposal, which comprises the following operations:
 etching the glass by means of a strongly alkaline compound, thus obtaining an aqueous-based liquid phase;   adding a sulphide to the so obtained liquid phase, with the precipitation of lead sulphide;   separating the solid lead sulphide from the above liquid phase.   
     
     
         2 . The process according to  claim 1 , wherein said alkaline compound is an alkali metal hydroxide. 
     
     
         3 . The process according to  claim 2 , wherein said compound is chosen from sodium hydroxide and potassium hydroxide. 
     
     
         4 . The process according to  claim 1 , wherein said glass etching operation is conducted by means of an aqueous solution of the alkaline compound at a temperature not higher than 200° C. 
     
     
         5 . The process according to  claim 4 , wherein the process temperature is higher than 100° C. 
     
     
         6 . The process according to  claim 5 , wherein the process temperature is between 150° C. and 180° C. 
     
     
         7 . The process according to  claim 1 , wherein the alkaline compound is employed in the form of an aqueous solution with a weight concentration between 10 and 50%. 
     
     
         8 . The process according to  claim 7 , wherein said concentration is between 15 and 45%. 
     
     
         9 . The process according to  claim 1 , wherein said glass etching operation is conducted by blending the glass with the alkaline compound in solid form, heating the so obtained solid mixture at a temperature higher than the melting temperature of the alkaline compound employed, and taking again the resulting molten mass with water. 
     
     
         10 . The process according to  claim 1 , wherein in said glass etching operation, the lead glass/alkaline compound weight ratio is between 1/0.6 and 1/1.4. 
     
     
         11 . The process according to  claim 10 , wherein said weight ratio is between 1/0.8 and 1/1.2. 
     
     
         12 . The process according to  claim 1 , wherein the glass is ground before said etching operation by the alkaline compound. 
     
     
         13 . The process according to  claim 1 , wherein said operation of adding a sulphide to the liquid phase is conducted by adding a water-soluble sulphide to said liquid phase, or by bubbling hydrogen sulphide therein. 
     
     
         14 . The process according to  claim 1 , wherein said operation of separating solid lead sulphide from the liquid phase is conducted by filtration or centrifugation. 
     
     
         15 . The process according to  claim 1  further comprising, after said operation of sulphide separation, a chemical analysis on said liquid phase, and:
 if, in the analysis, the presence of lead ions in the liquid phase is detected, a sulphide is added thereto in the form of a water-soluble salt, or by bubbling hydrogen sulphide therein; 
 if, in the analysis, the presence of sulphide ions in the liquid phase is detected, an effective oxidant for the oxidation of sulphide ion to sulphate ion is added thereto.