Metakaolin clay-derived geopolymer for recycling of waste cathode ray tube glass

Metakaolin clay (MC)-based geopolymer was used to immobilise waste cathode ray tube (CRT) glass as a method of recycling it into other useful products. Effects of CRT glass on the properties of geopolymer and toxicity status were assessed. A Nigerian MC was replaced with different proportions of ground waste CRT glass (0-20%) and alkali-activated to produce geopolymers. X-ray fluorescence (XRF) was used to characterise CRT and MC. The geopolymers were cured at room temperature for 7, 14, 21 and 28 days. Their setting time, compressive strength, dry density, water absorption and Pb binding abilities were evaluated. Geopolymers were leached using Toxicity Characteristics Leaching Procedure (TCLP). The XRF results revealed the main oxides of MC as SiO2 and Al2O3 and CRT glass as SiO2 and PbO. Setting time of the geopolymers ranged from 1 h (0% CRT) to 2 h (20% CRT). Compressive strength values of the geopolymers increased with percentage composition of CRT glass and curing age. At 28 days, the maximum compressive strength of 36.8±0.4 MPa was obtained for geopolymer that contained 20% CRT glass.  Increase addition of CRT glass reduced water absorption and increased the density of the geopolymer. Leachable Pb in the geopolymer extracts was below US EPA TCLP regulatory limit of 5 mg/L. Metakaolin clay geopolymers can be a cost-effective and sustainable binder to recycle CRT into value added products.   Key words: Metakaolin clay geopolymer, Immobilisation, cathode ray tube glass, recycling, leachable Pb.