Biomass of Desulfovibrio desulfuricans was used to recover Au(III) as Au(0) from test solutions and from waste electronic scrap leachate. Au(0) was precipitated extracellularly by a different mechanism from the biodeposition of Pd(0). The presence of Cu(2+) ( approximately 2000 mg/l) in the leachate inhibited the hydrogenase-mediated removal of Pd(II) but pre-palladisation of the cells in the absence of added Cu(2+) facilitated removal of Pd(II) from the leachate and more than 95% of the Pd(II) was removed autocatalytically from a test solution supplemented with Cu(II) and Pd(II). Metal recovery was demonstrated in a gas-lift electrobioreactor with electrochemically generated hydrogen, followed by precipitation of recovered metal under gravity. A 3-stage bioseparation process for the recovery of Au(III), Pd(II) and Cu(II) is proposed.

A B S T R A C TI t has been confirmed that the apparent rate constant for the reaction between methyl radicals, produced by the photolysis of deuterated acetone, and isobutane increases with decreasing isobutane pressure. A n explanation is proposed to account for this observation suggesting that the production of methane by disproportionation between methyl and t-butyl radicals was not negligible as has been assumed previously. I N T R O D U C T I O NObservations made recently in this laboratory indicated that values of the apparent rate constants for the abstraction of hydrogen by methyl radicals, calculated using conventional methods, depended on the pressure of the added hydrogen donor. The reaction of methyl radicals with isobutane using the pyrolysis of di-t-butyl peroxide a s a source of methyl radicals is an exanlple of such a system (I). When mixtures of deuterated acetone and hydrogen were photolyzed, the rate constant for the reaction of methyl radicals with hydrogen was found to be a function of the hydrogen pressure (2). In view of the apparent similarities between the two systems, an investigation of the photolysis of deuterated acetone -isobutane ~llixtures was made. E X P E R I M E N T A LThe apparatus and methods of analysis were similar to those employed in the photolysis of the deuterated acetone -hydrogen mixtures (2, 3). The deuterated acetone consisted of 98.2% acetone-ds and 1.8% acetone-d5. Phillips Research Grade isobutane was outgassed by bulb-to-bulb distillations a t -160" C. The temperature of the reaction cell was 471% 0.5" K for all experiments. R E S U L T S A N D DISCUSSIONIn the photolysis of mixtures of deuterated acetone and isobutane, it is usually assumed that methane and ethane are formed b y the following reactions:When the deuterated acetone was photolyzed alone ( 2 ) , small amounts of CD3H were formed due to the presence of acetone-d5 in the sample, and its yield was given bywhere [ A ] is the acetone concentration in molecules/cc. Allowance for this CDjH was made when calculating values of k,/kalt2.

The concentrations and the growth rates of high‐ and low‐melting type spherulites of trans‐1,4‐polyisoprene were measured in the temperature range 39–49°C. It was shown that above about 40°C., the crystallization rate of trans‐1,4‐polyisoprene is determined primarily by the radial growth rate of high‐melting form (HMF) spherulites, whereas the predominance of the low‐melting form (LMF) crystals below 40°C. can be attributed to the high rate of formation of LMF primary nuclei at lower crystallization temperatures. Temperature‐independent rate parameters were calculated from optical and dilatometric measurements and were found to be in good agreement. Both the change in nucleation habit and spherulite growth rate with temperature can be explained on the basis of a lower end surface free energy of LMF crystals of trans‐1,4‐polyisoprene compared to that of the HMF crystals.

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Stress–birefringence measurements have been made on a number of styrene–isoprene block copolymers, and their mechanical properties have been interpreted in terms of their molecular structures. Essentially, the polymers consist of highly dispersed phases of polystyrene and polyisoprene and undergo elastic deformation with the polystyrene domains acting as crosslinks. Hysteresis measurements have been carried out to interpret the stress–strain behavior of the polymers in more detail and the conformational properties of films prepared with selective solvents have also been examined with similar birefringence techniques.