Effect of waste plastics addition on the reduction of iron oxide by metallurgical coke

This work investigates the effect of waste plastics (high density polyethylene (HDPE)) addition on the production of premium grade iron nuggets from iron oxide using metallurgical coke as reducing agent. Composite pellets were formed from mixtures of iron oxide and carbonaceous materials consisting of coke, HDPE and three blends of coke-HDPE. The iron oxidecarbonaceous material composites were heated very rapidly in a laboratory scale horizontal tube furnace at 1500°C in a continuous stream of argon and the off gas was analysed continuously using an online infrared gas analyser and a gas chromatographic analyser. Elemental analyses of samples of the reduced metal were performed chemically for its carbon content and the extent of reduction was calculated based on a mass balance for removable oxygen. The results indicate that blending of coke with HDPE has the beneficial effect of improving the extent of reduction of iron oxide, with the time for complete reduction improving significantly from 600s (Coke) to 330s for Blends 1 and 2. Blending of coke with HDPE led to over 20% reduction in direct carbon dioxide emissions.Keywords: HDPE, coke, reduction, carburisation, iron oxid

Recycling Mixed Plastics Waste as Reductant in Ironmaking

One of the major obstacles to the implementation of an appropriate plastics recycling scheme is the inhomogeneity of many plastics waste. Accordingly, most of the existing recycling schemes require a feedstock that is reasonably pure and contains only items made from a single polymer type. However, in reality, waste plastics contain a mixture of plastic types, and are often contaminated with non-plastic items. This demands sorting out, which is expensive and highly labour intensive. In this work, the reduction of reagent grade iron oxide by mixed plastic waste (MPW) has been investigated through experiments conducted in a laboratory scale horizontal tube furnace. Composite pellets of reagent grade iron oxide (97 % Fe2O3) with MPW [consisting of 50 wt % high density polyethylene (HDPE), 30% polypropylene (PP), 10% low density polyethylene (LDPE) and 10% polyethylene terephthalate (PET)] were rapidly heated at 1520°C under high purity argon gas and the off gas was continuously analysed for CO, CO2 and CH4 using an online infrared gas analyser (IR). The extent of reduction after ten minutes was determined for each carbonaceous reductant and the results were compared with the extent of reduction by conventional metallurgical coke under the same experimental conditions. The results show that iron oxide can be effectively reduced to produce metallic iron using MPW as reductant. An improvement in extent of reduction was observed over metallurgical coke and the individual polymers when MPW was used as reductant. This eliminates the need to sort out individual plastics from municipal solid waste for their effective utilisation as reductants in ironmaking.Keywords: Reduction, Metallurgical coke, Mixed plastics waste, Extent of reductio

Microwave Production of Manganese from Manganese (IV) Oxide using Postconsumer Polypropylene as Reductant

This work investigates the production of manganese metal from MnO2 by microwave irradiation using postconsumer polypropylene (PP) as reductant. Reagent grade MnO2 was first calcined to Mn3O4 followed by reduction with pulverised PP in a domestic microwave oven (Pioneer, Model PM-25 L, 1000 W, 2.45 GHz) in a recorded temperature range 900-1200 °C. Calcined and reduced products were characterised by XRD, XRF and SEM/EDX. The results showed that microwave irradiation is effective at calcining MnO2 to Mn3O4, evidenced by the complete disappearance of peaks of MnO2 and appearance of peaks of Mn3O4 after 40 minutes. SEM/EDX analysis revealed that calcined Mn3O4 was first transformed to MnO and later to manganese metal. The range of temperature achieved in the microwave oven was below the equilibrium temperature for MnO reduction by solid carbon and accordingly solid carbon produced from PP cannot be wholly responsible for the production of manganese metal. It is therefore concluded that the production of manganese metal observed in this investigation was effected with CH4 (generated from the thermal decomposition of PP) and solid amorphous carbon as the predominant reductants, with solid amorphous carbon providing the heat energy required for the reduction. The reduction of manganese oxides using postconsumer plastics as reductants is therefore a potential route for diverting plastics from landfill sites as well as decrease the amount of expensive metallurgical coke currently used in the ferromanganese process.Keywords: Microwave irradiation, Polypropylene, Calcination, Reduction, Manganes

Carbothermal Upgrading of the Awaso Bauxite Ore using Waste Pure Water Sachets as Reductant*

Waste Pure Water Sachets (PWS) are currently among the fastest growing solid wastes generated in Ghana. Government’s attempt at banning its production and usage has been thwarted by the realisation that such a measure will increase the unemployment rate since the sachet water business employs a significant proportion of people. Meanwhile, the country currently exports its bauxite raw, without any value addition. Gradual depletion of high grade bauxite (with high alumina content) and the emergence of low grade bauxite with high iron oxide content calls for novel and inexpensive ways to upgrade these low ores. This project investigates a simple way of generating carbonaceous materials from PWS and their subsequent utilisation as reductants in the carbothermal upgrading of the Ghana Awaso bauxite. Samples of PWS were heat-treated in the temperature range 130-180 °C and the resulting molten material was cooled to render it brittle. The brittle mass was then pulverised and characterised by XRD and SEM. Composite pellets of bauxite sample and pulverised PWS were then formed, oven dried, placed in a fireclay crucible and heated in a gas-fired furnace. The magnetic fraction after reduction was separated by a Low Intensity Magnet and weighed. XRD analyses of the pulverised PWS showed peaks identical to those of high density polyethylene (HDPE). It was further observed that after about 30 min of firing, a large portion of the sample could be attracted by the magnet, indicating the suitability of the waste polymer as an important carbonaceous material for bauxite upgrading. The use of PWS as reductant prevented the formation of hercynite (FeAl2O4).Keywords: Pure water sachets, Bauxite, Gas-fired furnace, Magnetic fraction, High density polyethylen

Recycling Spent Primary Cells for the Synthesis of Spinel ZnMn2O4 using Waste Polypropylene as Reductant in a Microwave Oven

This work investigates the recycling of spent primary cells for the synthesis of spinel zinc manganese oxide (ZnMn2O4) using waste polypropylene as reductant in a domestic microwave oven. Spent zinc-carbon batteries (TigerHead brand) were cut into approximately two equal parts and the MnO2/Mn2O3/ZnO/carbon black mixture was carefully removed. The residual casing was dismantled and scrap iron, plastic and paper separated. The removed mixture was soaked in water for 24 hours after which it was filtered and the residue air-dried for 24 hours and pulverised in a mortar using a pestle. The pulverised mass was thoroughly mixed with pulverised polypropylene obtained from a mixture of waste bucket and the cap of the zinc-carbon battery. The mixture was then placed in a fireclay crucible and irradiated in a domestic microwave oven (Pioneer, Model PM-25 L, 2450 MHz, 1000 W) for 20 minutes and reaction products were separated and characterised. Spherical particles of spinel zinc manganese oxide (ZnMn2O4) were isolated after crushing the reduced mass. Analysis (XRD) of the residual reduced mass showed that it consisted of several peaks of ZnMn2O4 along with peaks of SiO2 and uncombined ZnO and Mn3O4.Keywords: Spinel ZnMn2O4, Primary cells, Zinc-carbon battery, Polypropylene, Microwave ove