Recovery of yttrium from fluorescent powder of cathode ray tube, CRT: Zn removal by sulphide precipitation

• Published in: Waste management (Elmsford) Vol. 33; no. 11; pp. 2364 - 2371
• Main Authors: Innocenzi, Valentina, De Michelis, Ida, Ferella, Francesco, Beolchini, Francesca, Kopacek, Bernd, Vegliò, Francesco
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.11.2013; Elsevier
• Subjects: Applied sciences; Cathode Ray Tube; CATHODE RAY TUBES; Cathode ray tubes (CRT); Chemical Precipitation; COPRECIPITATION; Electronic Waste; Exact sciences and technology; FLUORESCENCE; Fluorescent powder; HYDROGEN PEROXIDE; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LEACHING; MATERIALS RECOVERY; Other wastes and particular components of wastes; OXALIC ACID; PH VALUE; Pollution; PURIFICATION; REGRESSION ANALYSIS; SODIUM SULFIDES; SOLUTIONS; Sulfides - chemistry; SULFURIC ACID; Waste Products - analysis; Wastes; WEEE; YTTRIUM; Yttrium - isolation & purification; YTTRIUM OXIDES; ZINC; Zinc - isolation & purification; Zinc removal; ZINC SULFIDES; Zinc removal; Cathode ray tubes (CRT); Fluorescent powder; Yttrium; WEEE; Hydrogen peroxide; Cathode tube; Lixiviation; Regression analysis; Recycling; Mathematical model; Factorial design; Coprecipitation; Zinc
• DOI: 10.1016/j.wasman.2013.07.006
• ISSN: 0956-053X

•Treatment of fluorescent powder of CRT waste.•Factorial experimental designs to study acid leaching of fluorescent powder and the purification of leach liquors.•Recover of yttrium by precipitation using oxalic acid.•Suitable flowsheet to recover yttrium from fluorescent powder. This work is focused on the recovery of yttrium and zinc from fluorescent powder of cathode ray tube (CRT). Metals are extracted by sulphuric acid in the presence of hydrogen peroxide. Leaching tests are carried out according to a 22 full factorial plan and the highest extraction yields for yttrium and zinc equal to 100% are observed under the following conditions: 3M of sulphuric acid, 10% v/v of H2O2 concentrated solution at 30% v/v, 10% w/w pulp density, 70°C and 3h of reaction. Two series of precipitation tests for zinc are carried out: a 22 full factorial design and a completely randomized factorial design. In these series the factors investigated are pH of solution during the precipitation and the amount of sodium sulphide added to precipitate zinc sulphide. The data of these tests are used to describe two empirical mathematical models for zinc and yttrium precipitation yields by regression analysis. The highest precipitation yields for zinc are obtained under the following conditions: pH equal to 2–2.5% and 10–12%v/v of Na2S concentrated solution at 10%w/v. In these conditions the coprecipitation of yttrium is of 15–20%. Finally further yttrium precipitation experiments by oxalic acid on the residual solutions, after removing of zinc, show that yttrium could be recovered and calcined to obtain the final product as yttrium oxide. The achieved results allow to propose a CRT recycling process based on leaching of fluorescent powder from cathode ray tube and recovery of yttrium oxide after removing of zinc by precipitation. The final recovery of yttrium is 75–80%.