A novel approach for Ta and Nb extraction consisting of the pre-treatment of a coltan-bearing ore with an ammonium bifluoride sub-molten salt and subsequent acid leaching has been studied. The effects from ore granulometry, ammonium bifluoride (ABF) to ore mass ratio, temperature and duration of fluorination on the degree of Ta and Nb extraction were examined. The ABF to ore ratio and process temperature were found to have the most pronounced impact on extraction efficiency. The following optimal process conditions were determined: ore granulometric fraction (−75 + 45 µm), ABF-ore (5/1), fluorination temperature (200 °C) and fluorination time (2.5 h). Maintaining these parameters enabled about 94% of Ta and 95% of Nb to be brought into solution during the sulfuric-acid-leaching stage. A comparison of the proposed method with previously reported studies suggests that due to the effects of mechanical agitation and the recirculation of the HF-containing gaseous phase back into the process, the dosage rate of ABF at the fluorination stage could be reduced significantly without sacrificing the overall recovery of Ta and Nb. In such a way, the approach could offer added environmental benefits since release of fluoride-containing effluents into the environment could be limited.

The effect of varying process parameters during bio-catalyzed leaching of metals from end-of-life printed circuit boards (PCBs) was investigated. Fragmented PCBs (under 2 mm) were subjected to an indirect bioleaching in a stirred tank reactor while pulp density, pH and initial ferric iron content were varied. An iron oxidizing Acidithiobacillus ferrooxidans 61 microbial strain was used to generate the lixiviant through oxidizing Fe(II) to Fe(III). Chemically generated Fe(III) was tested as lixiviant under the same conditions as the biological one for comparative purposes. Cell enumeration during leaching and microscopic observations of the input and leached PCBs were conducted in parallel to shed light on the observed phenomena. The degree of bringing metals in solution was found to depend mainly on ferric iron concentration and pH. For the entire duration being always kept as 24 h, substantial portion of Cu (~87%) was extracted respectively at 1% pulp density (PD), 15.5 g/L Fe3+ and pH 1. For Zn and Ni, nearly 100% recovery was observed at 5% PD, 18 g/L Fe3+ and pH 1.1. The achieved results offer possibilities for further studies at higher pulp density, to ultimately render the bioleaching approach as enabling economical and environmentally friendly technology for urban mining of non-ferrous metals.

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The increased production and use of electrical and electronic equipment leads to obsolescence and disposal problems, necessitating materials recovery and recycling. This paper reports results on metal bioleaching from printed circuit boards (PCBs) using chemolithotrophic bacteria isolated at different sulphide ore biotopes in Armenia. Different ways of generating lixiviants were investigated, namely using combination of Acidithiobacillus ferrooxidans 61 and Acidithiobacillus thiooxidans SO-1 bacteria generating biogenic Fe 2 (SO 4 ) 3 and biogenic H 2 SO 4 . The sequence between these leaching agents permitted design of a 2-step process based on acidolysis and redoxolysis to leach non-ferrous metals from PCBs. To compare the efficiency of the sequential bioleaching of PCBs, several experimental runs were realised under the six modes at 10% pulp density. The flasks-based tests have witnessed almost complete recovery of Cu with the rest of the metals reaching extraction degree above 80%.