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- ItemMagnesium recovery from ferrochrome slag: kinetics and possible use in a circular economy(Heliyon, 2022-11-29) Moyo, L.B.; Simate, G.S.; Mamvura, T.A.The ever-increasing demand for ferrochrome alloys has resulted in a substantial accumulation of ferrochrome slag by-products in many mining areas. On the other hand, the ferrochrome slag has been identified as one waste material that is rich in magnesium (Mg) and has not been effectively exploited. Beneficiating of ferrochrome slag (FCS) waste material is envisaged as a means of achieving sustainable recovery of Mg. Previous studies have used sulphuric acid as a lixiviant for leaching FCS at moderate temperatures to recover Mg. In this study, the recovery of Mg from ferrochrome slag was investigated using hydrochloric acid (HCl) as the lixiviant at low temperatures. Previous studies have shown that various metal oxides have been proven to be more amenable to leaching using HCl. This study examined the effects of acid content, leaching temperature, and reaction time on the recovery of Mg from FCS. Kinetic and thermodynamic analysis of the leaching process were also investigated as these are critical factors for maximum extraction of the Mg. The results showed that the highest recovery of Mg of 88.2% was obtained from FCS using 5 M HCl with a solid to liquid ratio of 1:10, mixing intensity of 250 rpm, reaction time and temperature of 150 min and 70 C, respectively. The shrinking core model (SCM) was used in kinetic analysis to find the experimental data's best fit. A linear relationship was obtained with the coefficient of determination for the chemical reaction model (Kc) of >0.9 which indicates a good fit. The activation energy obtained for the diffusion and chemical reaction models were 95.44 and 41.45 kJ/mol, respectively, demonstrating that the rate-limiting phase is the one involving the chemical reaction.
- ItemBiological acidification of pig manure using banana peel waste to improve the dissolution of particulate phosphorus: A critical step for maximum phosphorus recovery as struvite(Heliyon, 2022-07-22) Moyo, L.B.; Simate, G.S.; Mutsatsa, T.Traditional disposal of agricultural bio-waste such as pig manure and banana peel waste poses an environmental nuisance. The uncontrolled disintegration of these waste materials decomposes to toxic effluent and methane a greenhouse gas twenty-one times more potent than carbon dioxide at trapping heat in the atmosphere, which is detrimental to the climate by elevating temperatures. Agricultural bio-waste is rich in nutrients that include nitrogen and phosphorus. Selectively separating these nutrients from the solid phase to produce high value products has been envisaged as an effective method of waste valorisation. This study aims to investigate the solubilisation of phosphorus (P) during anaerobic digestion (AD) of pig manure with banana peel waste as the co-substrate. The objective was to enhance the biological dissolution of the phosphorus from solid pig manure to the aqueous phase as this is envisaged to subsequently ease the recovery of P as a concentrated product via crystallization. Thereafter, phosphorus is used as a slow-release mineral fertilizer. Biological acidification was effective in reducing the pH to less than 6.50 from an initial pH of 7.28 at higher doses of BPW >100 g/L. Maximum dissolution of total phosphorus of 75% was observed at a pH of 5.40. Multiple regression analysis was used to correlate pH, banana peel waste concentration, and the anaerobic digestion time (ADT) to optimize the dissolution of P as this was deduced to be occurring at a low pH. A 2nd order polynomial was deduced to best fit the data with an R2 value of 0.90. The p values for the HRT and banana peel waste concentration were both <0.05 showing that both variables had a strong influence on the pH.
- ItemInvestigation on the Potential Production of Diesel from Waste Tires(Scientific Research Publishing, 2022-10-24) Mudono, S.; Jim, N.; Chigova, J.T.An alternative fuel production was performed by catalytic-pyrolysis of waste tires under a nitrogen (N2) environment and with a zeolite catalyst. Pyrolysis of scrap tires has been pointed out as an alternative to the incorrect disposal of tire wastes. Pyrolysis processes can produce tire-derived oils that may be used as fuel or added to conventional fuels, producing fuel blends with improved properties and reduced cost. The pyrolysis process can contribute to removing tire residues from inadequate sites and it can be a sustainable process to produce alternative fuels. The project investigated the conversion of the waste tires into diesel as one way of waste management and also as a viable process which in turn helps to meet the fuel demand. Uses of the diesel and the by-products from the process were also outlined. Experiments were conducted on the pyrolysis process in order to find the optimum conditions for producing the diesel through pyrolysis; the temperature and residence time were optimized in order to get maximum output from the process. The optimum temperature of the reaction was found to be 520˚C and the optimum residence time was 92.5 minutes. Quality tests of the product were then conducted on the obtained product and most of the properties were found to meet the required standard specifications. The most critical properties which are density, final boiling point, flash point and kinematic viscosity, were found to be 0.8495 g/cm3 , 370˚C, 50.5˚C and 3.681 cSt, respectively, and they were within the required specifications. Quality analysis showed that a quality product that is suitable for automobiles could be obtained from the process. The process also produces useful by- products such as char, which can aid in the purification process of the diesel after conversion to activated carbon. The process is environmentally friendly if the appropriate pollution prevention methods like gas absorption are thoroughly implemented. Waste tires are an alternative source of diesel and hence the feasibility of implementing the project on a large scale.
- ItemAdsorption of Chromium (VI) Using Nano-ZnO Doped Scrap Tire-Derived Activated Carbon(Scientific Research Publication, 2022-09-27) Chigova, J. T.; Mudono, S.Nowadays, nano mineral modified biochars show a promising adsorption capacity for pollutants removals by combining the advantages of porous structure of biochar and unique property of nano minerals. In this work, nanozinc oxide doped scrap tire derived activated carbon (nZnO-STAC) was synthesized by wetness impregnation method. Equilibrium data were analyzed using Langmuir and Freundlich isotherm models while the kinetics of the process were examined using Lagergren Pseudo-first and second order, intraparticle diffusion and Elovich kinetic models. Characterization of the activated carbon by Powder X-ray Diffraction (PXRD). The surface groups present on the activated carbon surface were determined using the Fourier Transform Infra-Red Spectroscopy (FTIR) analysis. Optimization studies were carried out to determine the effects of pH, initial metal concentration, adsorbent dosage, contact time and adsorbent particle size on the Cr (VI) removal efficiency. The results showed optimum Cr (VI) removal at pH 3, 10 mg/L concentration, 120 minutes of contact using 1000 - 1400 µm adsorbent particle size at a dosage of 2.5 g/L. The adsorbent structure was found to be predominantly amorphous. The chromium removal efficiency of the adsorbent was around 81.6%. Of the tested kinetic models, the pseudo-second order model exhibited the best fit with the experimental data with an R2 value of 0.9744. This study clearly demonstrates the feasibility of using the nano-ZnO doped scrap tyre derived activated carbon adsorbent for the remediation of chromium (VI) polluted industrial wastewaters.
- ItemTorrefaction of a mixture of animal waste and wood chips to produce sustainable bio coal: Kinetics and implications(2024) Tshuma, N.; Moyo, L.B.; Danha, G.; Mamvura, T; Geoffrey, S.; Artur, D.Perennial energy demands globally and the need to cut on fossil fuel based emissions has paved way for alternative energy sources such as raw biomass. However, raw biomass has faced challenges as a source of energy due to its low energy density and high moisture content compared to fossil coal. Consequently, pre-treatment of raw biomass has been deemed necessary to improve the aforementioned properties. The torrefaction process has been identified as an effective means to produce a sustainable solid fuel in the form of bio-coal from raw biomass. It is a promising technology that can be used to achieve a closed carbon cycle and mitigate greenhouse gas emissions. Characterization of bio-coal has shown comparative physical and chemical properties to fossil coal which can be synthesized by subjecting biomass to high-temperature thermo-chemical processing Biomass derived bio coal has shown excellent potential as a partial replacement for coal to achieve a closed carbon cycle and mitigate carbon dioxide emissions. Several drawbacks are associated with using animal waste as the sole feedstock for torrefaction processes. These issues encompass suboptimal energy yield, elevated ash levels and subpar bio coal quality. To counter these drawbacks, in this study, torrefaction on wood waste, animal waste and a mixture of the aforementioned materials at a ratio of 50: 50 by mass was investigated. The process conditions investigated included temperature and residence time intervals of 200 C to 500 C and 30 to 120 minutes respectively. The results showed that a positive adjustment in temperature and residence time increased the higher heating value (HHV) primarily due to release of moisture and volatile material. Wood and animal waste higher heating values were increased to 23.7 MJ/kg and 19.87 MJ/kg respectively from 17.9 MJ/Kg and 16.7 MJ/Kg respectively. Wood had a higher heating value upon treatment as the decomposition of hemicellulose and cellulose enhanced the thermal stability, fixed carbon content and calorific value. Whereas, animal waste had the least incremental increase in heating value due to a high initial content of volatile substances. The study showed that to overcome the drawbacks of having a low mass yield and heating value for animal waste, mixing animal waste with wood chips was effective in producing a product with a higher mass yield and calorific value. The kinetic analysis indicated that wood torrefaction is easily achievable compared to that of animal or mixed torrefaction as it had the lowest activation energy.