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- 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.
- ItemTreatment of efuent from a malting processing plant using bio‑coagulants(Discover Civil Engineering, 2024-07-05) Murisa, V.; Murisa, V.,; Ncube, S.; Moyo, L.B.; Danha, G.; Mamvura, T.A.Stringent measures by water authorities worldwide on water clarification has resulted in the use of chemical-based coagulants to be a formidable challenge. This has driven the need to find alternative sustainable coagulants such as plant-based bio coagulants which are readily available, abundant and cost effective in developing countries such as Zimbabwe. In this regard, the effectiveness of treating effluent from a brewery malting processing plant using bio-coagulants (Aloe Vera, Cactus opuntia and Okra seeds) was investigated compared to that of a chemical coagulant (Alum). The water pollution parameters that were investigated include turbidity, total dissolved solids, electrical conductivity, temperature and pH. The results showed that Alum was the most effective coagulant as it reduced the turbidity from 734 NTU to 68.3 NTU and Total Dissolved Solids (TDS) from 19,800 ppm to 880 ppm at a dosage of 40 mg/L. Okra seeds had an optimum dosage of 35 mg/L with a turbidity and TDS removal of 88.83% and 95.25% respectively. Aloe Vera had an optimum dosage of 40 mg/L with a turbidity and TDS removal of 74.25% and 95.40% respectively. For Cactus opuntia it was 50 mg/L obtaining turbidity and TDS removal of 74.66% and 95% respectively. The best blend of the bio coagulants had a ratio of (0.17, 0.17, and 0.67) for Aloe Vera, Cactus opuntia and Okra seeds respectively. At a dosage of 40 mg/L the turbidity removal was 83.92% and TDS removal was 95.12%. The results indicated that blending the plant-based coagulants had a positive synergistic effect. Highlights Aluminum sulphate (Alum) is more effective in reduction of suspended solids and dissolved solids compared to Aloe Vera, Cactus and Okra seeds. The effectiveness of Aloe Vera, Cactus and Okra seeds as plant-based coagulants indicates that they have active compounds effective as coagulation agents. There were positive synergistic effects upon blending Aloe Vera, Cactus and Okra seeds this was observed in the reduction of turbidity this was higher than when Aloe Vera and Cactus were used individually as coagulants.
- ItemCharacterization, kinetics and thermodynamic evaluation of struvite produced using ferrochrome slag as a magnesium source(South African Journal of Chemical Engineering, 2023-10-24) Moyo, L.B.; Simate, G.S.; Hobane, N.; Dube, C.There is limited data on studies that have focused on the kinetics, thermodynamics, and characterization of struvite crystallization from alternative magnesium sources. This study focused on thermal analysis of struvite (produced using ferrochrome slag as a magnesium source) and the results indicated that the residual quantities of struvite were lower than the theoretical mass loss of struvite of 51.42%. When using ferrochrome slag (FCS) as the magnesium source, 47.9%, 47.4%, and 46.9% losses in mass were observed for heating rates of 5◦C/min; 10◦C/min and 15◦C/min respectively. The mean activation energies for struvite produced using FCS were deduced using isoconversional kinetic methods and ranged from 49.81to 56.20 kJ/mol which is very similar to the activation energies deduced using MgCl2. The study also focused on the surface morphology, and particle size of the final product at different pH and N:P ratios. The final particle size distribution of the product was significantly influenced by the solution pH. To improve the crystal growth kinetics for both MgCl2 and FCS, a high ratio of N:P molar ratios should be adopted. The product's highest median particle size was obtained using FCS as the magnesium source at a low pH. Median particle size increased with decrease in pH, at a pH of 7.5 the recorded median particle size was 96 µ m whilst, the lowest was 31 µ m at a pH of 9.5. The highest percent of fines (<10 µ m) was recorded at a pH of 9.5 using FCS as magnesium source in the metastable region of struvite precipitation whereas at a pH of 7.5 no fines (<10 µ m) were recorded. SEM images confirmed that the struvite underwent morphological changes when prepared with FCS in comparison to that produced using MgCl2. The surface morphology of the finished product demonstrated the presence of irregular shaped particles, due to presence of impurities. The kinetic data showed that struvite precipitation was limited by the chemical reaction step. Model fitting was used to determine the reaction control mechanism and the average activation energies obtained by four model free methods were FWO (56.2), KAS (51.67) Starink (49.61) and Tang (49.81) kJ/mol, indicating that the FWO method was the least accurate method. The thermodynamic data indicated that the thermal degradation of struvite crystals has a high degree of disorder, and the process is endothermic, irreversible, and non-spontaneous.
- ItemKinetic and Equilibrium Modelling of Lead, Zinc and Copper Ions Sorption from Aqueous Solution Using Charcoal Fines(ournal of Applied Science and Technology (AJAST), 2024-06-30) Mungwari, C.P.; Chipangura, W.; Ndlovu, B.; Madziwa, T.N.; Simende, C.K.; Nyenyayi, K.; Chewu, C.C.The potential of chemically modified charcoal fines UCF (unmodified charcoal fine) and MCF (modified charcoal fines) as low cost adsorbents for the removal of Pb2+, Cu2+ and Zn2+ ions from aqueous solution was studied. MCF was prepared by chemical modification of UCF with HNO3 and KOH followed by pyrolysis. The factors influenced the effectiveness of biosorption process were pH, contact time, initial metal concentration, temperature and adsorbent dosage. FT–IR spectra confirmed the existence and interaction of the adsorbents with the effluent pollutants. MCF exhibited optimum pH, temperature, contact time, initial metal ion concentration and biosorbent dosage values of 5, 35 0C, 90 minutes, 15 mg/L and 2 g, respectively. UCF exhibited optimum pH, temperature, contact time, initial metal ion concentration and biosorbent dosage values of 6, 35 0C, 100 minutes, 20 mg/L and 2.5 g, respectively. The adsorption isotherm modelling using both adsorbents showed that the equilibrium data conformed more to Langmuir than the Freundlich model. Kinetic studies showed that the adsorption processes followed a pseudo-second order kinetic model. Thermodynamic studies confirmed the spontaneity and feasibility of the adsorption process. The results showed that both adsorbent have the potential to be applied as alternative low cost biosorbent.