PROCESSING OF SPENT ULTRA-DEEP HYDRODESULFURIZATION CATALYSTS. This work discusses the recycling of spent NiMo/Al2O3 catalysts from ultra-deep hydrodesulfurization (HDS) units. They contain a refractory coke and fouling elements from the processed feedstocks. Samples were preoxidized (600 ºC) for 12 h using a very slow heating rate to eliminate coke and volatiles. Experiments were performed in the presence of HF + H2O2 mixtures under stirring at 25-60oC for 1-4 h. The amount of insoluble matter was the lowest (< 1 wt.% of the initial mass) after leaching for 2 h at 60oC using an excess of 50 vol.% HF and 20 vol.% H2O2. Leached molybdenum and vanadium were extracted together with Alamine 304 (tri-dodecylamine) in n-heptane at pH below 2. Aluminum and iron were precipitated from the raffinate as Na3AℓF6 (+ Na3FeF6) by adjusting pH at ~4 using 6 mol L-1 NaOH. Nickel was either recovered by solvent extraction using D2EHPA (bis-(2-ethylhexyl)phosphoric acid) in n-heptane at pH 6 or precipitated at pH 8 using 6 mol L-1 NaOH. The first method proved better as less contaminants were present. After slow evaporation of the final aqueous solution, a mixture of Na2SiF6 and NaF was recovered. Fluoride losses were very low (~0.10 wt.%).

The recovery of precious and base metals of a metal concentrate from ground waste printed circuit boards (PCBs) is described in detail. Samples were treated with NaOHaq. to remove the soldering mask. Experiments were performed in acidic medium (HF, H2SO4, CH3COOH or H3PO4) using H2O2 as oxidant. Base metals were leached in high yields (>99 wt.%) at ~40 ºC after ~1 h (HF), ~2 h (H2SO4), ~4 h (H3PO4) and ~5 h (CH3COOH). Lead precipitated in the presence of H2SO4 and HF. Precious metals were not oxidized. Ceramic/fiberglass components were dissolved in the presence of HF. Silver, palladium and gold were recovered from the insoluble solid, in this order, by a sequential oxidative treatment in aqueous medium. Recovery of leached elements was possible by a combination of solvent extraction and precipitation. The choice of the extractant and the precipitant were essential to recover them with high yields. The leachates from H3PO4 + H2O2 experiments could not be processed above pH 2.5. Leaching of waste PCBs in the presence of a weak organic acid is possible but a multistage separation scheme for elements recovery is unavoidable as PCBs is a complex material in terms of composition.

This work examines the leaching of printed circuit boards (PCBs) from cell phones in aqueous solutions containing HF + H2O2 or HF + NaClO under mild experimental conditions. The PCBs were not ground but were previously treated with 6 mol L-1 NaOH at 50 ºC for 1 h to remove their soldering mask. The HF + H2O2 mixtures leached copper and base metals (except lead) at 35-40 ºC, leaving a solid residue containing lead and noble metals. Leaching was fastest (1 h) when HF and H2O2 concentrations were at least 5 mol L-1 and 3 mol L-1, respectively. The processing of the solid residue is also described in detail. It was leached with water at ~90 ºC followed by HNO3aq. at 25 ºC. Lead, palladium and silver were recovered in this order, leaving gold as final solid. After 1 h at 35-40 ºC, 5 mol L-1 HF + 0.3 mol L-1 NaClO mixtures leached the base metals, copper, gold and palladium. Gold was recovered by liquid-liquid extraction with methyl isobutyl ketone. Silver precipitated as chloride. This salt was isolated by leaching with NH3aq. Loss of fluoride ions (as HF) was below 0.5 wt.% after leaching and handling the solid residue.

This paper describes a route for recovering manganese and zinc from spent zinc-MnO2 dry cells via acid leaching using sulfuric or hydrochloric acids as leachants. Hydrogen peroxide was added as reductant. Experiments were run at 25-40 °C for 1-3 h. Under the best optimal conditions, over 97.5 wt.% of zinc and manganese were leached by both acids. Zn(II) was best extracted at high free acidity (≥ 1 mol L-1) with tributylphosphate (TBP) or trialkylphosphine oxides (Cyanex 923) diluted in n-heptane. Cyanex 923 was a better extractant than TBP, and the extraction was better performed in hydrochloric leachates. Mn(II) was more co-extracted from hydrochloric leachates and when Cyanex 923 was the extractant, but was easily scrubbed with dilute leachant (~1-2 mol L-1). Zn(II) striping was possible using 5 mol L-1 HCl or H2SO4. Manganese was precipitated as oxalate (MnC2O4.2H2O), free of leached contaminants. High-purity sodium salts of the anions of the leachants were recovered after slow evaporation of the final solution.