Ferromanganese and zinc production with pyrometallurgical method from spent alkaline batteries

Battery is a device which turns chemical energy directly to electrical energy. First battery is made from Alessandro Volta and Luigi Galvani. Industrial battery use became available with Michael Faraday. Battery use became more common with increasing electrical device usage. Batteries made most of the electrical devices mobile. Mobile energy storage advantage made batteries very popular. Since battery usage increased battery waste is also increased. Rechargeable batteries, secondary batteries, could be reusable again with charging but single use batteries, primary batteries, are waste batteries after use. In today‟s world, battery industry, reached over millions of metric tonnes of battery production. Waste battery levels are parallel with increasing battery production and use. In 2012, European waste battery amount was about 250.000 metric tonnes. Waste batteries are not ordinary waste and should be taken care with specially. In European Union 2006/66/EC directive is published and taken into action by European Parliament. Control of Waste Batteries and Accumulators Directive taken into action in 2015, in Turkey. These directives regulated batteries, heavy metal contents of batteries, battery waste and recycling techniques. These regulations made battery collection and recycling mandatory for producers and encouraged private sector for recycling plants. Waste batteries are hazardous to environment with their metal content and basic or acidic electrolyte. These compounds can be hazardous to soil and under water supplies. Furthermore waste batteries are containing valuable metals inside and these metals should be recovered. Waste battery recycling is both economically and environmentally mandatory. In this study, alkaline spent batteries are researched. Alkaline batteries are containing potassium hydroxide as electrolyte, gelled zinc powder as anode and manganese dioxide as cathode materials. At first existing recycling technologies for primary batteries are researched. Pyrometallurgical processes are dominant in primary battery recycling. Basically in primer batteries recycling with pyrometallurgical method high vapour pressure metals are vaporized and metal is collected as condensed or oxidized powder henceforth left over metals are smelted and mostly ferroalloys produced to be sold to xviii steel producers. Hydrometallugical techniques are not in use industrially for primary batteries. As the second step chemical analysis, XRD analysis and thermodynamic researches are conducted. Determining elements and phases of spent alkaline batteries is the first step of research. After determining phases and elements in spent alkaline batteries thermodynamic research is done. Process and reactions to produce metals are designed according to compounds and thermodynamic data of compounds. Production and recovery steps of potassium hydroxide, zinc, manganese and steel are defined. A flow sheet of process is proposed. According to process planning spent alkaline batteries firstly mechanically crushed grinded and sieved. Battery paste and steel cover is separated. Battery paste is washed with water in order to eliminate potassium hydroxide. After that step battery powder is filtered and dried. Battery paste is prepared for further processing to recover zinc from it. For zinc recovery, a stainless steel reaction vessel is used. Vessel is designed and produced for zinc recovery specially. Potassium hydroxide recovered battery paste is mixed with coke coal and placed into the reaction vessel then placed in to furnace. Experiments for zinc recovery are performed with Argon gas at various temperatures and different experiment times. Reaction gas is passed through a gas cleaning system and gas contains zinc vapour is washed down. The water used in gas cleaning then used to prepare a solution of sulphuric acid to solve zinc in acid. Zinc recovery is researched under given conditions. Manganese dioxide and steel is smelted under slag in reductive conditions in order to produce ferromanganese alloy. Smelting is performed in an electric resistance furnace with addition of flux agents. Ferromanganese alloy then examined with optical microscope, scanning electron microscope, micro hardness testing machine. Results are discussed for the offered process conditions. As a result potassium hydroxide is recovered to some extent. Recovery conditions of potassium hydroxide were not suitable for recovery of all potassium hydroxide in spent alkaline batteries. Possible improving conditions are offered for further researches. Zinc recovery is examined in two steps. First step of process is reductive conditions for zinc and separating zinc from battery paste. At this point study was very promising and results showed that zinc oxide can be reduced to the zinc metal and vaporized. Chemical analysis of samples showed zinc could be separated almost completely under certain conditions. On the other hand zinc recovery rate was not coherent to zinc evaporation rate. Possible conditions caused to that incoherency between zinc evaporation step and recovery step is explained in this study. For the last step of recycling process battery paste is mixed with steel cover and coke, lime stone, fluspar and silica added to graphite crucible. Crucible is placed in to furnace and heated to decided smelting temperature. After smelting is done crucible is cooled down in furnace and then metal and slag is taken out of crucible. Ferromanganese alloy is examined for micro structure, chemical analysis and micro hardness. Results showed that produced alloy is not commercial ferromanganese but a promising master alloy which can be used in ferromanganese production or can be improved to commercial grade ferromanganese. As a result, this study showed that spent alkaline batteries can be used in potassium hydroxide, zinc and ferromanganese production. Improvements suggested can be useful for other researchers who are considering further research on this topic. Recycling of spent alkaline batteries with pyrometallurgical method is possible. If economic conditions are adjusted feasibly production of zinc and ferromanganese from spent alkaline batteries with pyrometallurgical method could be a environmentally friendly technology.