Extraction of Gold from Alkaline Gold Leaching Solution by Tertiary Amine N235 and Phosphine Oxide
Extraction of gold from alkaline gold leaching solution by N235-TRPO synergistic system was studied. The effects of the concentrations of Tri-akylphosphine oxide(TRPO)and tertiary amine(N235), the initial pH, and the concentration of gold on the extraction of gold and the extraction isotherm were inspected. The ability of extracting other metal elements by this system had been investigated. The effect of alkali concentration on stripping of gold from loaded organic phase had also been studied. The experimental results indicate that the system consisting of 10% N235, 10% TRPO gave high extraction yield for gold along with the lesser extraction of silver and copper which are needed to recover. The gold extraction was over 94%, at pH=9~10 and the stripping of gold from loaded organic phase using 0.05mol/L NaOH can reach91.43%.
Synergism in gold–cyanide extraction with Primene JMT–Cyanex 925 mixed extractant system
Abstract The synergic extraction of gold (I) from cyanide solutions has been studied using a mixture of Primene JMT (primary amine=RNH 2 ) and Cyanex 925 (bis(2,4,4,trimethylpentylactyPhosphine oxide=R 3 PO) in xylene. The variables that could affect the extraction system were investigated: equilibration time, temperature, aqueous pH, extractant mixture concentration, metal concentration and organic phase diluent. The selectivity of the system with respect to the extraction of different metal–cyano complexes was also evaluated. The gold (I) extraction reaction is discussed on the basis of the experimental results and numerical treatment of the experimental data. The species formed in the organic phase have the probable stoichiometry H + Au(CN) 2 − RNH 2 (R 3 PO) n , n being 1 (log K ext =10.27 max 10.55) or 3 (log K ext =12.80±0.13). Stripping of gold from loaded organic solutions was also studied using low ionic strength alkaline solutions at different experimental conditions.
Variations of sulphur dioxide at the cloud top of Venus’s dynamic atmosphere
A pulse of sulphur dioxide in Venus’s upper atmosphere was observed by the Pioneer Venus spacecraft in the 1970s and 1980s and attributed to volcanism. Recent sulphur dioxide measurements from Venus Express indicate decadal-scale fluctuations in sulphur dioxide above Venus’s cloud tops in an atmosphere that is more dynamic than expected. Sulphur dioxide is a million times more abundant in the atmosphere of Venus than that of Earth, possibly as a result of volcanism on Venus within the past billion years1,2. A tenfold decrease in sulphur dioxide column density above Venus’s clouds measured by the Pioneer Venus spacecraft during the 1970s and 1980s has been interpreted as decline following an episode of volcanogenic upwelling from the lower atmosphere3,4. Here we report that the sulphur dioxide column density above Venus’s clouds decreased by an order of magnitude between 2007 and 2012 using ultraviolet spectrometer data from the SPICAV instrument onboard the Venus Express spacecraft. This decline is similar to observations during the 1980s. We also report strong latitudinal and temporal variability in sulphur dioxide column density that is consistent with supply fluctuations from the lower atmosphere. We suggest that episodic sulphur dioxide injections to the cloud tops may be caused either by periods of increased buoyancy of volcanic plumes, or, in the absence of active volcanism, by long-period oscillations of the general atmospheric circulation. The 30-year observational record from Pioneer Venus and Venus Express confirms that episodic injections of sulphur dioxide above the clouds recur on decadal timescales, suggesting a more variable atmosphere than expected.