Recovery of base metals, silicon and fluoride ions from mobile phone printed circuit boards after leaching with hydrogen fluoride and hydrogen peroxide mixtures

• Published in: Waste management (Elmsford) 2018-08, Vol.78, p.781-788
• Main Authors: Silva, Walner Costa, de Souza Corrêa, Roger, da Silva, Calvin Sampaio Moreira, Afonso, Júlio Carlos, da Silva, Rubens Souza, Vianna, Cláudio Augusto, Mantovano, José Luiz
• Format: Article
• Language: English
• Subjects: Copper recovery; Elements separation; Fluoride salts; PCBs; Solvent extraction
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2018.06.049

•Separation of elements complexed by fluoride ions via precipitation or crystallization.•Recovery of non complexed metal ions via SX with D2EHPA at very different pH.•Very low losses of fluoride ions after leaching and during leachate handling.•Low final wastes generation. The recovery of copper, nickel, zinc, silicon, iron, aluminum, tin and fluoride ions from fluoride leach liquors of non-ground printed circuit boards (PCBs) from mobile phones is described in detail. These PCBs were leached with HF + H2O2 mixtures after previous treatment with 6 mol L−1 NaOH (removal of the solder mask). A combination of solvent extraction (SX) and precipitation techniques was used. 99.5 wt% zinc, copper and nickel, in this order, were extracted in one stage (Zn, Ni) or two stages (Cu) with di-2-ethylhexylphosphoric acid (D2EHPA) diluted in kerosene (25 °C, A/O = 1 v/v) after adjusting the pH of the leachate. They were easily stripped by aqueous H2SO4. Iron, aluminum and tin did not interfere because they were masked by fluoride ions. Iron and aluminum were precipitated together as Na3FeF6 + Na3AlF6 by careful addition of aqueous NaOH. Silicon, tin and fluoride ions were recovered together (Na2SiF6 + Na2SnF6 + NaF) by careful evaporation of the aqueous solution after SX of nickel. The tin salt was leached from this solid by absolute ethanol. High HF concentration (10 mol L−1) in the leachant affected SX of Cu(II) and precipitation of iron/aluminum flurocomplexes since some NaF partially precipitated at acidic pH.