A novel electrobiotechnology for the recovery of precious metals from spent automotive catalysts

Platinum group metals are routinely used in automotive catalysts but recycle technology lags behind demand. There is no available 'dean technology' and leach solutions (e.g. aqua regia) to solubilise the metals from scrap are highly aggressive. A microwave-assisted leaching method was developed which gave 80% metals recovery, with the leach time reduced from 2 h to 15 min using 50% (aq.) diluted aqua regia to give potentially a more biocompatible leachate. Desulfovibrio desulfuricans reduces soluble platinum group metals to cell-bound insoluble base metals (e.g. Pd(II) --> Pd(0)). For use, biofilm was immobilised on a Pd-23% Ag solid alloy membrane which delivered H. to the cells via an electrochemical chamber at the back-side. The biomass-coated Pd-Ag alloy electrode was used in a flow-through reactor for recovery of Pd, Pt and Rh from aqua regia leachates (pH 2.5) of spent automotive catalysts with up to 90% efficiency at a flow residence time of 15 minutes. Free cells did not reduce platinum group metals from the leachates but the electrobioreactor did so using biofilm-cells pre-loaded with Pd(0). Reactors lacking biomass or reactors with heat-killed biofilm removed less platinum group metals, via electrochemically-synthesised H. reductant alone. The use of an active biofilm layer in a flow-through electrobioreactor provides a simple, dean and rapid potential recycle technology.

The Processing of Beach Sand from Sri Lanka for the Recovery of Titanium Using Magnetic Separation

An investigation has been carried out to study the mineralogical and chemical characteristics of beach sand deposits from Sri Lanka and application and optimisation of different magnetic separators (induced roll magnetic separator and disc magnetic separator) to improve the recovery of titanium from the deposit. Commercial grade titanium concentrates could be achieved employing both induced roll and disc magnetic separators. However, the titanium recovery increased greatly in the magnetic fraction with a titanium content of commercial grade (up to 63.9% TiO2) when paramagnetic titanium-bearing minerals were separated from beach sand using the disc magnetic separator. The results of the mineralogical and chemical analysis tests for the beach sand deposit indicated that 71% of beach sand was smaller than 355 μm in particle size and more than 99% of titanium content of the deposit was contained in this fraction.

The Effect of Heat Treatment on Chalcopyrite

The influence of conventional heat treatment and microwave radiation on chalcopyrite was investigated. There was a significant increase in the proportion of material recovered to magnetic fraction and magnetic susceptibility with conventional heating time. XRD analysis detected phase changes in conventional heat-treated chalcopyrite, which increases the magnetic susceptibility of the ore and enables its effective magnetic separation, which is impossible to achieve in its original state.

With microwave treatment, the magnetic susceptibility increases and the proportion of material recovered to magnetic fraction on the induced rolls is also increased. However, XRD analysis failed to detect any phase changes. A possible explanation for this observed behaviour is that the more magnetic component that has been formed by microwave treatment is below the threshold of detection of the XRD analyser. Taking into account that results from the froth flotation tests indicated that % weight fraction in the concentrate decreases with microwave exposure time, the change might be due to a surface effect.

The effect of microwave radiation on the magnetic properties of minerals

The effects of microwave radiation on the magnetic properties of common ore minerals are discussed. The effects of varying microwave power levels on heating rates are presented along with comparative magnetic susceptibility surveys for both treated and non treated minerals. Various chemical and physical analysis techniques are considered to quantify any changes in mineral phases during heating. Conclusions are made as to the possible impact of microwave pretreatment on the downstream magnetic processing of minerals and ores.