Browsing by Author "Paiva, A. P."
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- Oxidative leaching process with cupric ion in hydrochloric acid media for recovery of Pd and Rh from spent catalytic convertersPublication . Nogueira, C. A.; Paiva, A. P.; Oliveira, P. C.; Costa, Maria Clara; Costa, Ana M. Rosa daThe recycling of platinum-group metals from wastes such as autocatalytic converters is getting growing attention due to the scarcity of these precious metals and the market pressure originated by increase of demand in current and emerging applications. Hydrometallurgical treatment of such wastes is an alternative way to the most usual pyrometallurgical processes based on smelter operations. This paper focuses on the development of a leaching process using cupric chloride as oxidising agent, in HCl media, for recovery of palladium and rhodium from a spent catalyst. The chloride media allows the adequate conditions for oxidising and solubilising the metals, as demonstrated by equilibrium calculations based on thermodynamic data. The experimental study of the leaching process revealed that Pd solubilisation is clearly easier than that of Rh. The factors temperature, time, and HCl and Cu(2+) concentrations were significant regarding Pd and Rh leaching, the latter requiring higher factor values to achieve the same results. Leaching yields of 95% Pd and 86% Rh were achieved under optimised conditions (T = 80 °C, t = 4h, [HCl] = 6M, [Cu(2+)] = 0.3M).
- Separation and recovery of Pd and Fe as nanosized metal sulphides by combining solvent extraction with biological strategies based on the use of sulphate-reducing bacteriaPublication . Nanusha, Mulatu Yohannes; Carlier, Jorge; Carvalho, Goncalo Ivo; Clara Costa, Maria; Paiva, A. P.Platinum group metals (PGMs) are highly demanding metals in current high-techs. However, their supply is limited due to their scarcity in natural resources and expensive mining. Solvent extraction in combination with microbial communities were employed for the recovery of palladium from aqueous media. Accordingly, extraction of Pd(II) by N,N'-dimethyl-N,N'-dicyclohexylthiodiglycolamide (DMDCHTDGA) in toluene and subsequent stripping by acidic thiourea were carried out, followed by bio-recovery employing biogenic sulphide generated from sulphate-reducing bacteria. The results revealed an excellent extraction performance of DMD-CHTDGA towards Pd(II) from metal complex mixtures in 2,4 and 6 M HCl. However, Fe(III) was co-extracted from 4 and 6 M HCl, being completely removed with deionized water during scrubbing. 94-99% of extracted Pd (II) were stripped using acidic thiourea. Over 99% of stripped Pd(II) were recovered using two solutions containing biogenic sulphide: an effluent from a bioremediation process of acid mine drainage treatment, and a supernatant solution from Postgate B nutrient medium. 78-99% of scrubbed Fe(III) were bio-recovered. Analysis of all the precipitates collected during palladium bio-recovery showed that they were composed by Pd and S, which is consistent with the synthesis of nanosized PdS. The elemental analysis of the iron precipitate also suggests the presence of iron sulphide. Henceforth, the method engaged is environmentally sustainable, safe and cheap, thus attractive to be employed, to separate and recover both Pd and Fe from waste materials.