Recovery of metallic values that random access memory chips contain via hydrometallurgical treatments

Especially after the 1980s, with the development of informatics technologies, worldwide production and consumption of electrical and electronic devices increased rapidly, while their useful life decreased. Since the electrical and electronics industry has the World's largest and fastest growing production capacity, it became difficult to follow up the newly developing technology as their technological properties worn out quickly. As the gap between the functional and technological lifetimes of electric and electronic components widen rapidly these devices become obsolete. The amount of electrical and electronic equipment waste (e-waste), such as computers, mobile phones, large and small-scale household appliances etc. is measured by the millions of tons, and increasing every year, causing a serious solid waste problem. Electrical and electronic equipment waste contains organic and inorganic components and is quite different from other solid wastes. The common disposal method for e-waste is either burning or landfilling both of which cause environmental pollution and economical losses. E-waste includes base metals; such as copper, iron, nickel, zinc, and precious metals; such as gold, silver, palladium. In addition to glass, ceramic and plastic, e-waste may also contain heavy metals (mercury, cadmium, lead, barium, tin), fluorocarbons, chlorinated and brominated flame retardants, containing numerous toxins that are harmful to the environment. Besides its environmental perspective, recycling of electrical and electronic goods is also a must economically. The recycling of WEEE minimizes the volume of landfill and ease the pollution of soil, ground water, surface water and air due to the release of hazardous components. Printed circuit boards are base part of electric and electronic equipments and contain major fraction of metals present in e-wastes. Printed circuit boards are especially rich in copper and precious metals such as gold, silver and palladium. Recovery are performed on most printed circuit boards due to the rich copper and precious metal content. In order to recovery of base and precious metals from electric and electronic equipments, some treatments such as physical, pyrometallurgical, biometallurgical and hydrometallurgical processes are proposed. In the pyrometallurgical process, the solid wastes are melted with flux components. Molten slag containing precious metals forms a pool into which the precious metals dissolve and accumulate. The molten metal is called a collector metal. Widely used collector metals contain Fe, Cu, Ni, Pb-Cu, and Ni matte. The extracted precious metals must be further treated to severally separate and purify them. In the past two decades, the most active research area on recovery of metals from electronic scraps is recovering precious metals by hydrometallurgical techniques. Comparing with the pyrometallurgical processing, hydrometallurgical method is more exact, more predictable, and more easily controlled. Featured processing, "mechanical crushing and hydrometallurgical" is still the most competitive technology for waste PCBs recycling, and it is the most commonly used technology to recovery of metals from printed circuit boards. The aim of this thesis, from the economical and environmental perspective, is to recycle via physical and hydrometallurgical routes and to reveal the process flow scheme for RAMs (Random Access Memories), a crucial component of modern day computers.. For this purpose, upon the removal of solder, crushing, grinding, and magnetic seperation, waste RAMs are treated chemically with either nitric acid, hydrocholoric acid, and/or aqua regia. Precious metals which are in solution recovered with cementation and gold precipitation processes. RAMs used in this are supplied in cooperation with Kadıköy Electronic Waste Collection Centre. First solders were removed with heat treatment. The furnace was heated to 200-220°C and RAMs kept for 20 minutes at the furnace. To avoid harmful gas output, temperature was not get higher. With this process RAMs were separeted into two main parts namely the printed circuit boards and integrated. Crushing and grinding processes were performed both printed circuit boards and integrated samples and particle sizes of these samples were found 13 and 16 micron respectively. Chemical composition of two samples was analyzed using inductively coupled plasma-mass spectrometer (ICP-MS) and X-ray fluoresence spectrometer (XRF). Testing apparatus was prepared before leaching treatments. Testing apparatus was composed of 1 litre 3 necked reactor, stirrer, glass screw for srtirring, heater and thermocouple. The opening at the center of reactor eas fitted with polymer. Condenser were also employed to avoid reagent evaporation. In the nitric acid leaching, to find the optimum conditions 1M, 3M, 5M and 10M acid concentrations; 45oC, 55oC and 65oC temperatures; 1/10 and 1/20 solid/liquid ratio parameters tested while 200 rpm stirring speed and 500 ml solution volume and 2 hours reaction time were kept constant. Firstly, 500 ml nitric acid solution of a known concentration was added into the reactor, and heated to required temperature with heater. To minimise the effect of exothermic reaction and to avoid excessive agitation due to the realise of nitrous oxide fumes, desired amount of samples were added to solution in small increments. 5ml samples were collected at intervals of 5, 15, 30, 45, 60, 90 and 120 minutes and stored at 50 ml volumetric flaks. The concentration of copper in solution was measured by Atomic Absorption Spectrometry. The best conditions for leaching of Cu and Ag in nitric acid leaching system were determined to be 5M HNO3, at 55oC for 2 hours with a solid/liquid ratio of 1/20. Dissolution rates of 97.4% Cu was achieved under these conditions. Aqua regia is a combination of three parts of concentrated hydrocloric acid and one part of concentrated nitric acid. The strong oxidising and reducing properties of this reagent allowed complete dissolution of precious metals. In aqua regia leaching, to find the optimum conditions 40 ml, 120 ml and 200 ml acid concentrations; 35°C and 55°C temperatures parameters tested while 200 rpm stirring speed and 500 ml solution volume and 2 hours reaction time were kept constant. Before aqua regia leaching, solution was fresh prepared, it was added into the reactor, and heated to desired temperature with heater and samples were added solution in small increments. 5ml samples were collected at intervals of 60, 90 and 120 minutes and stored at 50 ml volumetric flaks. The concentration of gold in solution was measured by Atomic Absorption Spectrometry. The best conditions for leaching of Au in aqua regia leaching system were determined to be 200 ml acid concentration and 55°C temperature. Dissolution rates of %43.6 for pcb samples and %21.1 for entegre samples were achieved under these conditions.