Leaching and Adsorption of Gold from Waste Printed Circuit Boards Using Iodine-Iodide Solution and Activated Carbon
Iodine-iodide leaching and activated carbon adsorption processes for recovery of gold (Au) from waste printed circuit boards (WPCBs) were discussed in this paper. A pressure oxidative acid leaching (POAC) was carried out in an autoclave using diluted sulfuric acid (1M H 2 SO 4 ) solution in order to remove high concentrations of some base metals especially copper (Cu), aluminum (Al), iron (Fe) and zinc (Zn) due to their negative effect on gold dissolution from WPCBs. The factors affecting the performance and efficiency of the iodine-iodide leaching process; such as iodine/iodide concentration, pulp density, leaching time and leaching temperature were optimized in order to maximize the gold dissolution efficiency from the WPCBs in the iodine-iodide solution. Results indicated that the vast majority (> 99%) of gold was dissolved in the solution from the WPCBs under the optimized leaching conditions. Adsorption tests were conducted on leach liquor solutions resulting from the iodine-iodide leaching using activated carbon. Nearly 98% of gold was adsorbed from the liquor solution onto the carbon under the condition optimized in this study. The results obtained revealed that gold can be successfully recovered from this secondary resources, where the percent recovery amounts to nearly 97% for gold.
Recovery of Valuable Metals from Waste Printed Circuit Boards by Using Iodine-Iodide Leaching and Precipitation
This study presents a viable approach for recovery of precious metals such as gold (Au), silver (Ag), palladium (Pd), and base metals, including copper (Cu), nickel (Ni), cobalt (Co), lead (Pb) and zinc (Zn) from waste printed circuit boards (WPCBs) via iodine-iodide leaching and precipitation. The behaviours of dissolution and precipitation of precious and base metals during iodine-iodide leaching and precipitation processes were discussed. Sodium hydroxide (NaOH) was used to remove base metal impurities exist in the pregnant leach solution under alkaline conditions. Precious metals remained in the resulting solution from NaOH precipitation were recovered by reduction using ascorbic acid (L-AA) solution. Results show that under optimum leaching conditions, almost all (> 99%) of Au was dissolved in an iodine-iodide solution when the dissolution efficiencies of other precious metals (Ag, Pd) and base metals, besides calcium (leaching of 25%) were less than 1 and 6%, respectively. The study revealed that more than 95% of Cu, Ni, Pb, Zn, Fe and Mn were initially removed from the pregnant leach solution at pH of 9.3 with addition of 0.1 M NaOH. Then 99.8% Au, 81.7% Ag and 74% Pd were precipitated from the obtained solution after NaOH precipitation while L-AA dose was 0.6 ml/ml at the condition. It can be concluded that the precious and base metals could be recovered selectively and economically from WPCBs via iodine-iodide leaching followed by precipitation using NaOH and L-AA.
The evaluation of the competency perception of inspectors in using new instructional technology
Abstract The purpose of this study is to find out the evaluation of inspectors in regards to their competency perceptions towards the use of new instructional technologies. This is a qualitative model research. The target population of this study consisted of 25 inspectors serving within the borders of TRNC in 2011. Data was collected by an “interview form” developed by the researcher. The interview form consisted of 6 items. Content analyze, frequency (f) and percentage (%) techniques were used to analyze the data. This research pointed out that: “concerns on falling behind the teacher”, “training needs”, “decreasing training support within the years” and “non existing policy on IT support” are critical factors affecting an inspector's competency perceptions in using new instructional technologies.