Loss Of Precious Metals Research Articles

Hydrometallurgical processing of waste multilayer ceramic capacitors (MLCCs) to recover silver and palladium

Present paper reports an application oriented approach to recover precious metals such as silver (Ag) and palladium (Pd) from multilayer ceramic capacitors (MLCCs) of waste printed circuit boards (PCBs). These capacitors are being widely used in modern electronic gadgets to provide advance features as well as to enhance their performance. Due to the generation of large amount of e-waste as well as the loss of precious metals, a sincere R&D effort has been made to develop a process for the recovery of Ag and Pd from waste MLCCs. Initially, the MLCCs were depopulated from the PCBs by de-soldering using thermal treatment. Further, the depopulated material was pulverised to get homogeneous fine powder of MLCCs, which contained 0.14% Pd, 1.08% Ag, 1.76% Cu and 11.1% Ni. First of all Ni was removed/recovered selectively using two stages of leaching at optimized condition i.e. 2 M HCl, temperature 75 °C and pulp density 100 g/L. The obtained leached residue was washed, dried and further leached to get 99.99% Ag and Pd both in solution using 4 M HNO3, temperature 80 °C, pulp density 100 g/L and mixing time 1 h. From the obtained leach liquor, salt of Ag (purity 99.99%) was selectively recovered/precipitated using KCl. Further, Cu was extracted from the Ag depleted solution using LIX 84IC leaving Pd in the raffinate, which was evaporated to get pure Pd salt. The developed flow-sheet has potential to be commercialized after scale up trials.

Recycling of gold from waste electronic components of devices

Tremendous generation of e-waste and its illegal recycling are causing immense threat to environment as well as the loss of precious metals. The present research reports a novel hybrid process for the total recovery of gold from small depopulated components of e-waste. Connectors and integrated circuits (ICs) liberated from printed circuit boards (PCBs) were pulverized and processed for gold leaching using 10 g/L sodium cyanide solution at 40 °C and mixing time 15 min, where more than 95% gold was found to be leached out in single stage. From the obtained leach liquor, gold metal was recovered by charcoal adsorption followed by heat treatment. The raffinate left after adsorption of gold was found to contain ~10 mg/L gold, which was also recovered using Amberlite IRA 400Cl at equilibrium pH 9.6 in 30 min maintaining aqueous/resin (A/R) ratio 25 mL/g. The raffinate solution was enriched to 882.41 mg/L and the solution was further processed to get metal/salt using cementation/ evaporation. Obtained leached residue is processed for non-ferrous metals recovery and finally disposed-off after treatment and TCLP test. The effluent left after leaching could be easily decomposed and treated in ETP using standard environmental procedure.

Solar photovoltaic panels as next generation waste: a review

Photovoltaic energy manufacturing has developed at an extraordinary rate since the last decade which globally has reached 225 giga watts by 2018 and is anticipated to augment to 920 giga watts by 2022 and 5000 giga watts by 2050. Still now the abundant quantity of produced solid waste which comes from the end of life panels are not calculated yet but in future it can be a challenging aspect in terms of photovoltaic energy. Harmful waste from end of life solar panels poses a global ecological menace and is capable of creating 300 times more toxic waste than nuclear plants. This review represents an overview of global scenario on different types of solar panels production with their composition, applications, solid waste generation, loss of precious metals (rare earth metals, metals), utilization of metals in different industries and different toxicological effects on the environment and the requirement of recycling of used solar panels. The recycling of these solar panels after life can be an economic alternative source of natural resources.

Homogeneous versus Supported ONN Pincer‐Type Gold and Palladium Complexes: Catalytic Activity

The ONN-tridentate unsymmetrical pincer-type (S)-1-((6-(2-hydroxyphenyl)pyridin-2-yl)methyl)-N-methyl-N-(3-(triethoxysilyl)pro-pyl)pyrrolidine-2-carboxamide ligand has been synthesized by an easy method, in high purity and good yield. Its respective palladium(II) and gold(III) complexes have been prepared as air-stable solids. After deprotonation of the -OH group the coordination of the metal ion is completely stereospecific and gives rise to only one diastereoisomer. The complexes, immobilized onto ordered mesoporous silica (MCM-41), are shown to be very active catalysts in the hydrogenation of prochiral olefins (98% ee was achieved with the heterogenized chiral Au(MCM-41) complex), hydrosilylation, and Suzuki and Heck C-C coupling reactions, under mild conditions. The reactions were studied with the soluble catalysts as well as their heterogenized counterparts. The high accessibility introduced by the structure of the supports allows the preparation of highly efficient immobilized catalysts. The repeated use of the immobilized catalyst in four cycles demonstrates "homogeneous" catalysis with "heterogeneous" catalysts, thus reducing solvent waste and loss of precious metal and/or ligand.

BINAP-Ru and -Rh catalysts covalently immobilised on silica and their repeated application in asymmetric hydrogenation

We present the facile immobilisation of a chiral diphosphine ligand, BINAP, on a silica (high pore volume, low surface area). The protected ligand has been immobilised as a phosphine oxide and deprotected on the surface to prevent side reactions of unprotected phosphines with surface silanol groups. The resulting diphosphine ligand on silica was converted to both rhodium and ruthenium complexes. The novel materials were characterised using solid-state IR-DRIFT and 29Si and 31P CP-MAS NMR techniques as well as elemental content measurements. Ruthenium and rhodium catalysed asymmetric hydrogenation of various enamides, β-keto-esters and aromatic ketones is presented using immobilised BINAP ligands. The repeated use of the immobilised catalyst in five recycles demonstrates ‘homogeneous’ catalysis with ‘heterogeneous’ catalysts, thus reducing solvent waste, and loss of precious metal and or ligand.

Loss of precious metal from Pt-Rh alloy under refractory oxide environments

Loss of precious metals from a Pt-10 wt% Rh alloy was studied at 1300° C in refractory oxides and fused quartz environments. After 60 and 150 h annealings, samples exposed to gaseous environments showed significant weight loss. The surface was attacked and characterized by micron-sized pits, as well as river-like striations. The pits were found to be enriched with silicon and/or aluminium depending upon the heating environment. Laser Raman microprobe identified that the major compound formed in the pits is α-cristobalite.

IX.—On certain sources of loss of precious metal in some operations of assaying

IX.—On certain sources of loss of precious metal in some operations of assaying