Journal Articles


Recent Submissions

Now showing 1 - 20 of 160
  • Item
    Kinetics, adsorption isotherms, thermodynamics, and desorption studies of cadmium removal from aqueous solutions using bamboo sawdust/rice husk biochar
    (Springer Nature, 2022) Kwikima, Muhajir Mussa; Chebude, Yonas; Meshesha, Beteley Tekola
    The adsorption mechanisms of Cd2+ removal from synthetic water using blended biochar from bamboo sawdust (BSD) and rice husk (RH) feedstocks at BSD/RH ratios 1:1, 1:3, and 3:1 were investigated. The equilibrium isotherms (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich) and kinetics (pseudo-first order, pseudo-second order, Elovich, and intra-particle diffusion kinetic adsorption models) and thermodynamics were examined. The BSD/RH biochar ratio of 1:1, 1:3, and 3:1 produced the Cd2+ removal of 99.2%, 98.3%, and 97.24% respectively. The adsorption investigation found insignificant differences in removal efficiency across the biochar ratio combinations. Furthermore, the equilibrium isotherm analyses for the BSD/RH ratio of 3:1 and 1:1 are best described by in favor of the Freundlich model, whereas for BSD/RH biochar ratio of 1:3 best matched the Langmuir model. The thermodynamic study revealed that the process is non-spontaneous, endothermic, and dominated by the physisorption mechanism. Generally, physisorption was discovered to be the dominant process controlling the Cd2+ removal from the solution.
  • Item
    Parents’ practices associated with aflatoxin contamination and control of complementary foods in Central Tanzania
    (Science Publishing Group, 2016) Ngoma, Selestin; Tiisekwa, Bendantukuka; Mwaseba, Dismas; Kimanya, Martin
    Parents’ practices that are associated with aflatoxin contamination and control in complementary foods were studied in Central Tanzania. A descriptive cross-sectional survey using interviewer-administered structured pretested questionnaire was conducted among 364 randomly selected parents of children aged between 6-23 months, and the mean age (SD) of the respondents was 30 (8.3) years old. The majority 33.2% of the participants harvest their crops in April followed by June which is 26.6%, March which is 21.2% and May which is 19% of all the participants. Most processing activities like dehulling, milling, drying, storage were analysed. The statistical packages SPSS (version 21) computer software packages were used to analyze the data. The results of logistic regression model for dehulling crops confirmed that respondents with less than or with US$ 22.8 as monthly income (OR=0.250, 95% CI: 0.111-0.564) were significantly 0.3 less likely to dehull crops (p<0.05) than respondents who earned more than US$. 22.8. On the other hand, petty trader participants (OR =3.712, 95% CI: 1.420-9.699) were significantly almost 4 times more with a tendency of dehulling the crops (p<0.05) than farmers. The study team recommends that parents should be trained on appropriate methods of drying, storage, and dehulling their crops after harvesting in order to control fungal and aflatoxin infestation. In addition, research on harvesting time, drying, storage, and dehulling practices of crops in Tanzanian is needed
  • Item
    Application of machine learning in the prediction of compressive, and shear bond strengths from the experimental data in oil well cement at 80 °C. Ensemble trees boosting approach
    (Elsevier, 2022) Nyakilla, Edwin E.; Jun, Gu; Kasimu, Naswibu A.; Robert, Edwin F.; Innocent, Ndikubwimana; Mohamedy, Thamudi; Shaame, Mbarouk; Ngata, Mbega Ramadhani; Mabeyo, Petro E.
    The current study aimed at predicting shear bond strength (SBS) and compressive strength (CS) using ensemble techniques of gradient boosting regression tree (GBRT) from the experimental data. Experimental data were obtained from CS and SBS studies using class F fly ash as supplementary cementitious materials at different proportions. The experimental results showed that the application of class F fly ash increases both CS and SBS with curing time due to the pozzolanic action of the fly ash. The SBS and CS for 15% replacement after 28 days were 0.353 and 41.9 MPa, respectively compared to 0.324 and 39.5 Mpa for 30% fly ash. This means higher fly ash content decreases both CS and SBS. Cement, OWC, water, fly ash, curing time, and dispersant were set as input data for machine learning (ML) while experimental SBS and CS as output. ML results showed that GBRT overperformed Artificial neural network (ANN), support vector machine (SVM), and Gaussian process regression (GPR)models since it gave the greatest R2 = 0.995 for CS, 0.989 for SBS and the least loss functions (MSE = 0.160 , MAE = 0.174), and (MSE = 0.0005 , MAE = 0.0031) for CS and SBS, respectively.. The comparative findings of both experimental and estimation, therefore affirm that for the long life of oil and gas wells, GBRT can be implemented as an improved approach for cement hydration prediction.
  • Item
    Review of developments in nanotechnology application for formation damage control
    (American Chemical Society, 2022) Ngata, Mbega Ramadhani; Yang, Baolin; Aminu, Mohammed Dahiru; Iddphonce, Raphael; Omari, Athumani; Shaame, Mbarouk; Nyakilla, Edwin E.; Mwakateba, Imani Asukile; Mwakipunda, Grant Charles; Yanyi-Akofur, David
    Formation damage has the potential to impair and weaken reservoir productivity and injectivity, causing substantial economic losses. Oil and gas wells can be damaged by various mechanisms, such as solid invasion, rock–fluid incompatibilities, fluid–fluid incompatibilities, and phase trapping/blocking, which can reduce natural permeability of oil and gas near the wellbore zone. These can happen during most field operations, including drilling operations, completion, production, stimulation, and enhanced oil recovery (EOR). Numerous studies have been undertaken in recent years on the application of nanotechnology to aid the control of formation damage. This review has found that nanotechnology is more successful than traditional materials in controlling formation damages in different phases of oil and gas development. This is facilitated by their small size and high surface area/volume ratio, which increase reactivity and interactivity to the adjacent materials/surfaces. Furthermore, adding hydrophilic nanoparticles (0.05wt %) to surfactants during EOR alters their wettability from 15 to 33%. Wettability alteration capabilities of nanoparticles are also exemplified by carbonate rock from oil-wet to water-wet after the concentration of 4 g/L silica nanoparticles is added. In addition, mixing nanoparticles to the drilling fluid reduced 70% of fluid loss. However, the mechanisms of impairment of conductivity in shale/tight formations are not consistent and can differ from one formation to another as a result of a high level of subsurface heterogeneity. Thus, the reactivity and interaction of nanoparticles in these shale/tight formations have not been clearly explained, and a recommendation is made for further investigations. We also recommend more nanotechnology field trials for future research because deductions from current studies are insufficient. This review provides more insights on the applications of nanoparticles in different stages of oil and gas development, increasing our understanding on the measures to control formation damage
  • Item
    Evaluation of rainfall extreme characteristics in Dodoma urban, a central part of Tanzania
    (2022) Mdee, Ombeni J.
    The occurrence of low rainfall in semi-arid areas including Dodoma urban leads to a shortage of water. This paper addresses the evaluation of rainfall extreme characteristics by analyzing the variability indices, probability distribution, and return periods. The daily rainfall index shown the magnitude of rainfall varied unpredictably within annual wetted days. The study area experienced a period of one to two months per year with extreme seasonality as evaluated using the rainfall seasonality index. The standardized anomaly index indicated the equivalent of 60% of 20 years experienced the dried years with unpredicted occurrence. The Weibull distribution was selected out of Fifteen probability functions when ranked using Kolmogorov–Smirnov and Anderson-Darling tests. The return periods of rainfall had an average rainfall of 576 mm and were predicted using seventeen plotting position methods and Weibull distribution. Therefore, the magnitude of rainfall in the semi-arid areas would not easily be estimated but using more than one technique would improve the evaluation of rainfall characteristics
  • Item
    Fluoride occurrence in domestic water supply sources in Tanzania: a case of Meru district Arusha region
    (University of Dar es Salaam, 2018) Mbabaye, Godfrey; Minja, Rwaichi; Mtalo, Felix; Legonda, Isacka; Mkongo, Godfrey
    Surface and ground water are the major sources of water supply in Meru district. Most of the people in Meru rural areas depend on surface water in rivers and ground water shallow and deep wells and springs for house hold activities. The presence of fluoride in high concentrations in drinking water or cooking water causes severe health problems to the people. Distribution of fluoride concentrations in Meru district domestic water sources was studied by referencing the location of water sources using Extrex 20 garmin hand held GPS instrument. Fluoride concentrations were measured using Metrohm Ag/AgCl reference electrode connected to a Metrohm potentiometer (826 pH/Ion Meter) in a laboratory. Fluoride concentrations were found to range between 0.76 and 1103 mg/L. Around 69% of 146 samples collected had fluoride concentrations above 1.5 mg/L which is the WHO recommended standard while 47% of the samples had fluoride concentrations exceeding 4.0 mg/L as recommended by the Tanzania Bureau of Standards. The results indicate that, residences in five wards of Meru district namely Kikatiti, King’ori, Leguruki, MajiyaChai, and Ngarenanyuki are exposed to high levels of fluoride posing risk of dental and skeletal fluorosis. Generally, the study observed that most of the ground and surface water resources in Meru district are contaminated with high fluoride concentration and therefore waters from most sources in the areas (wards) need to be defluoridated to be potable.
  • Item
    Use of phyto-based polymeric material as chemical admixture in well cement slurry formulation
    (Elsevier, 2021) Lupyana, Samwel Daud; Sahini, Mtabazi Geofrey; Kattiba, Saada Msafiri; Gu, Jun
    Plants extracts contain a wide range of organic components and have been used as admixtures in modifying different cement properties. In this study, aqueous extract of Euphorbia Tirucalli (ET) as bio-admixture was characterized and tested for potential use in the preparation of well cement slurry. Several tests such as setting time tests, fluid loss tests, rheological properties of well cement slurries incorporating different proportions of the ET and the reference slurries without ET were conducted and evaluated. Phytochemical composition of ET was investigated by using Gas Chromatography-Mass Spectrometer (GCMS) analytical technique. Interactions between the bio-admixture and cement components during hydration were also characterized by Fourier Transform-Infrared (FT-IR) spectroscopic technique. GC–MS analysis indicates the presence of the palmitic acid groups such as hexadecanoic acid, methyl ester, n-Hexadecanoic acid and 9-Hexadecanoilc acid and the fatty acid components commonly known as linoleic acid. Incorporation of the bio-admixture shows to enhance fluid loss properties and slurry rheology. Also, the bio-admixture indicates promoting retardation of cement hydration due to increase in setting times with increase in mix proportions. These properties indicated to be dependent to the bio-admixture concentration. FT-IR spectroscopic investigations suggests possible interaction between bio-admixture and the ionic species in the cement slurry.
  • Item
    Overview of microwave-assisted transesterification technology for biodiesel production with bibliometric indicators
    (Tylor & Francis, 2022) Kombe, Godlisten Gladstone
    The demand for novel, environmentally sustainable biodiesel intensification technologies is growing. Microwave-assisted transesterification technology is one potential solution to this gap. This study evaluates the research productivity of microwave-assisted transesterification technology for biodiesel production using various bibliometric indicators. Using relevant keywords search, data were extracted from the Scopus database. Visualization of similarities viewer (VOSviewer) software v1.6.18 was then used for network visualisation and various bibliometric analysis. The study shows that microwave-assisted transesterification technology is still in its early stages when compared to other biodiesel production technologies. Despite the fact that its potential was first highlighted in 2004, the first study on its application was published in 2007. However, it was not until 2010 that several researchers became interested in this technology. The most productive countries in publications, existing collaborations and cooperation, top institutions in publications, and top journals have been identified and presented. Finally, keyword co-occurrence analysis of the subject, as well as the most prolific researchers and the highest referenced publications in the field, were presented and discussed. Researchers are likely to benefit from the study's bibliometric indicators in finding prospective research topics, high-quality scientific literature, and relevant journals for disseminating research related to microwave-assisted transesterification technology for biodiesel production
  • Item
    Perspective and control of cation interdiffusion and interface reactions in solid oxide fuel cells (SOFCs)
    (Elsevier, 2023) Sahini, Mtabazi Geofrey; Lupyana, Samwel Daud
    The occurrence of cation interdiffusion during sintering and operation of Solid Oxide Fuel Cells (SOFCs) is inevitable, due to high temperatures and chemical potential gradients. Cation interdiffusion may be followed by solid state reaction, resulting into the formation of secondary phases. Understanding of the factors that trigger the occurrence of cation interdiffusion and interface reactions is crucial towards controlling their occurrences. Here, we have discussed the phenomena associated with cation interdiffusion in solid oxide fuel cells. We have established that cation interdiffusion and interface reactions occur both during the high temperature sintering and during SOFC operations. Case examples where cation interdiffusion and subsequent interface reactions form secondary phases are discussed. The various methods that can be used to minimize or control the occurrence of cation interdiffusion are discussed: the use of diffusion barriers, fabrication of strontium free cathode materials, lowering the sintering temperature and the SOFC operating temperature
  • Item
    Glycerolysis of high free fatty acid oil by heterogeneous catalyst for biodiesel production
    (Elsevier, 2022) Selemani, Asumin; Kombe, Godlisten G.
    The most widely used commercial biodiesel production technique, alkali-catalysed transesterification, requires only moderate temperatures and pressures to achieve a more than 98% conversion yield. Unfortunately, oil feedstock’s high free fatty acid (FFA) content limits the technology’s usefulness. A heterogeneous base catalysed glycerolysis process was investigated in this study to lower the FFA and meet these requirements. The response surface methodology (RSM) based on I-optimal design was used to model and optimize a CaO catalysed glycerolysis reaction under the influence of five reaction variables: temperature (60–180 ◦C), residence time (30–120 min), FFA concentration (6–50%), catalyst amount (0.4–0.6 wt (g/g)), and Glycerol to Oil ratio (G/O) (1–1.5). The data were fitted in a quadratic model, and R2 of 0.986 was observed, signifying that the model well defined the experimental data. The model was validated by running four replicates of the experiment, and a residual standard error of 2.7% was obtained, indicating the model would accurately predict future observations. The 48.584% FFA in oil was reduced to 0.98% under optimal conditions of 170 ◦C, 39.9 min of residence time, 0.591wt g catalyst concentration, and 1.026 g/g glycerol/oil (G/O) ratio. CaO catalysed glycerolysis has significantly reduced FFA to less than 3% in less than an hour in biodiesel feedstock for biodiesel production.
  • Item
    Analysis of performance characteristics predicted from several experimental data and conversion methods for pumps as turbine application using statistical techniques
    (University of Dar es Salaam, 2020) Mdee, Ombeni J.; Kimambo, Cuthbert Z. M.; Nielsen, Torbjorn K.; Kihedu, Joseph
    Different performance characteristics have been indicated when running centrifugal pumps in the reverse direction. The water flows from the discharge side of the pump to the suction side to run in the reverse direction and generate the mechanical rotational energy for the micro-hydropower plant. The current study evaluates the extent of variation of performance characteristics predicted by several experimental data from different pump-specific speeds and conversion methods. The performance characteristics discussed include the head, flow rate, efficiency and specific speed. The flow rate and head of a pump operating in pump mode divided with the characteristic of the pump operating in the reverse mode, at the best efficiency point, the resulting coefficient of determination (R 2 ) values were of 0.890 and 0.708, respectively. Also, the graph of head versus flow rate coefficients, which is a second- order polynomial function, has shown the value of R 2 of 0.954 for pump-specific speed ranging between 9 and 94 rpm. However, the pump in the reverse mode has smaller performance characteristics for efficiency and specific speed compared to the pump mode operation with R 2 of 0.966 and 0.999, respectively. Furthermore, schematic empirical statistical models were developed to predict the performance characteristics of several conversion methods using pump data obtained from the manufacturers.
  • Item
    Solvent extraction of Jatropha oil for biodiesel production: effects of solvent-to-solid ratio, particle size, type of solvent, extraction time, and temperature on oil yield
    (Hindawi, 2021) Ntalikwa, Justin W.
    The aim of this study was to examine the effects of solvent-to-solid ratio, particle size, extraction time, and temperature on the extraction of Jatropha oil using three organic solvents, i.e., n-hexane, petroleum ether, and ethanol. The Soxhlet extraction method was used, and the parameters were varied in the following ranges: extraction temperature of 24–80°C, extraction time of 2 to 8 h, solvent-to-solid ratio of 4 : 1 to 7 : 1, and particle size of 0.5–0.8 mm. After obtaining optimal conditions, a large volume of Jatropha oil was prepared, purified, and subjected to analysis of quality parameters. It was found that the oil content of the Jatropha curcas L. seeds used was 48.2 ± 0.12% w/w. The highest oil yield of 47.5 ± 0.11% w/w corresponding to an oil recovery of 98.6 ± 0.3% w/w was obtained with n-hexane under the following conditions: solvent-to-solid ratio of 6 : 1, particle size of 0.5–0.8 mm, extraction time of 7 h, and extraction temperature of 68°C. This was followed by that of petroleum ether (46.2 ± 0.15% w/w) and lastly by ethanol (43 ± 0.18% w/w). The quality parameters of the oil extracted compared favorably well with most of the values reported in the literature, suggesting that the oil was of good quality for biodiesel production. Environmental and safety concerns over the use of hexane pose a great challenge. Thus, ethanol, which is environmentally benign, is recommended for application. The conditions for ethanol extraction that gave high oil yield were as follows: extraction temperature of 70°C, extraction time of 7 h, solvent-to-solid ratio of 6 : 1, particle size of 0.5–0.8 mm, and oil yield of 43 ± 0.18% w/w corresponding to an oil recovery of 89.2 ± 0.4% w/w.
  • Item
    Pulping sisal fibres: effects of chemical concentration, na2so3/na2co3 ratio and fiber to chemical ratio
    (University of Dar es Salaam, 1994) Katima, J.H.Y.; Halfani, M.R.; Ntalikwa, J.W.
    This paper reports on pulping of hard fibres extracted from the leaves of agave sisalana using sodium sulphite buffered with sodium carbonate as pulping chemical. The cooking was carried out at I68C for a cooking period of 6 hours, with varying chemical concentration, sodium sulphite to sodium carbonate ratio and fibre to chemical ratio. The results show that both the pulp yield and pulp viscovity decrease with increasing chemical concentration, whereas Kappa number of pulp decreases to a limit of about 16.45. Brightness increases significantly with an increase in the ratio of Na3SO/Na2CO3. The pulp yield obtained indicated the following maximum strength indices: tensile index: 75.60/Nm/gJ, burst index: 6.05/kPa. m2/g/and tear index: 19.30/Nm2/kg). These values are higher than those reported for bleached pine kraft pulp; that is tensile index: 50.52/Nm/g), burst index: 5.77/kPam2/g/and tear index: 18.91/Nm2/kg) with a brightness of 81.0% ISO. These make sisal a promising candidate for non-wood pulping process.
  • Item
    A review of intermediate pyrolysis as a technology of biomass conversion for coproduction of biooil and adsorption biochar
    (Hindawi, 2021) Kazawadi, Deodatus; Ntalikwa, Justin; Kombe, Godlisten
    The agenda to utilize and efficiently convert biomass has been raised to alleviate environmental problems and pressure on the reliance on fossil fuel. Intermediate pyrolysis has the ability to treat different biomasses and coproduction of biooil and adsorption biochar. This review article aims to evaluate the appropriateness of intermediate pyrolysis for the coproduction of biooil and adsorption biochar. It was observed that coproduced biooil is of high quality, stable, and miscible that can be used directly to existing engines or be easily blended. The biochar coproduced is good for adsorption but is not stable for microbial attack and hence unsuitable in soil treatment but for hydrometallurgy. Since the process is capable of treating waste biomass, it is an opportunity for further investigations in areas where wastes are plenty and less utilized. To increase the effectiveness of this technology for coproduction, optimizing parameters, design of efficient reactors, and use of catalyst must be worked upon
  • Item
    Evaluation of pollution loading into Msimbazi river by rapid assessment and direct measurement methods
    (University of Dar es Salaam, 2018) Katima, J.H.Y.; Mbele, H.O.; Ntalika, J.W.
    This paper assesses the suitability of Rapid Assessment (RA) methodology as 4 tool for making an environmental pollution inventory in data poor situation. The W4 method was applied to estimate Biological Orygen Demand (BOD), nitrogen an phosphorous loading into the Msimbazi River in Dar es salaam, Tanzania. The Pree/Measurement (DM) was done to validate the results obtained from RA. The methodologis based on estimating waste loads from function variables such as production rale. population, etc. and pollution intensities from domestic, industry and agricultural sources. The incorporation ofpenetration factors for waste loads reduction refines the assessmen/procedure. The RA results show that domestic source releases 7600, 390 and 3200 tons/year of BOD, Phosphorous and Nitrogen respectively. Industrial activities in the area release BOD loading of 2500 tons/year
  • Item
    Optimization of biodiesel production from jatropha oil
    (Trans Tech Publications Ltd., 2010) Okullo, Aldo; Temu, A.K.; Ntalikwa, J.W.; Ogwok, P.
    The most important factors that influence biodiesel production are temperature, molar ratio, catalyst amount, time and degree of agitation. This study investigated the effects of temperature, molar ratio and degree of agitation and their interactions on the yield and purity of biodiesel produced from Jatropha oil. Factorial design and response surface methodology (RSM) were used to predict yield and purity of biodiesel as functions of the three variables. Interactions of all the factors were found to be significant on both yield and purity responses. Temperature and molar ratio main effects were found to be significant on the yield whereas only temperature main effect was significant on the purity of the biodiesel. The optimum conditions of operations were; temperature of 54 oC, molar ratio of methanol to oil of 6:1 and stirring speed of 660 rpm. Using these conditions, biodiesel yield of 95% (wt) was obtained with a purity of 97%. This model can be used to predict the yield and purity of biodiesel from jatropha oil within the ranges of temperature (30 – 60oC), stirring rate (300 -900 rpm), and molar ratio (3 – 9 mol/mol) studied.
  • Item
    An overview of algae for biodiesel production using bibliometric indicators
    (Hindawi, 2023)
    Algae are a desirable biodiesel feedstock because they take up little space, have a high algal-cell biomass per unit area, and can sustainably meet a large portion of the world’s future energy needs. Using several bibliometric indicators, this study assesses the research productivity of algae for biodiesel production. The dataset was retrieved from the Scopus database using anappropriate keyword search. The VOSviewer v1.6.18 and Biblioshiny in R-studio were then utilised for bibliometric analysis and network visualisation. The study found that, with the first article being published in 1990 and an annual scientific growth rate of 14.76%, research on algae for the generation of biodiesel is still in its early phases. Although the possibility of utilising algae to produce biodiesel was originally mentioned in 1990, it was only until 2006 that several researchers started to show an interest in the subject. 101 articles were published in 2015, which is the most ever. The most prolific countries in terms of publications, ongoing collaborations and cooperation, best publishing institutions, and prestigious journals, as well as the most productive researchers and the most highly referenced works in the field, have all been recognised and presented. Finally, a keyword co-occurrence analysis of the subject was presented and discussed to provide research insights into the field. The bibliometric indicators of the study are intended to aid researchers in finding potential research topics, high-quality scientific literature, and suitable journals for publishing research on algae for biodiesel production.
  • Item
    Gas chromatographic determination of glycerol and triglycerides in biodiesel from jatropha and castor vegetable oils
    (Trans Tech Publications Ltd., 2013) Okullo, Apita, Aldo; Ogwok, P; Temu, Abraham K.; Ntalikwa, J.W.
    Monoacylglycerols and diacylglycerols are intermediate compounds in biodiesel which result from incomplete transesterification reaction during biodiesel production. Traces of free glycerine and partially reacted triacylglycerols are also found in biodiesel. These contaminants cause serious operational problems in engines, such as engine deposits, filter plugging, and emissions of hazardous gasses. Increased levels of these contaminants in biodiesel compromise quality which is vital for commercialisation of this product. In this work, levels of free glycerine and total glycerine in jatropha methyl ester (JME) and castor methyl ester (CME) were determined using gas chromatography (GC) equipment. Amounts of free and total glycerine in JME and CME were generally high compared to the ASTM D6751 and EN14214 recommended values. Free glycerine from JME was 0.1% wt compared to 0.02% wt (ASTM D6751) and 0.01% wt (EN14214) values whereas the total glycerine from JME was 2.96% wt compared to 0.24 %wt (ASTM D6751) and 0.21% wt (EN14214). These discrepancies could have resulted from insufficient purification of the product and incomplete conversion or due to the high temperature associated with GC analysis that might have caused pyrolysis or thermal degradation of certain lipid components. Castor methyl ester free glycerine was 0.14% wt while total glycerine was 13.21% wt. This can still be explained by the same reasons given for JME. Thermal decomposition of lipid components in a GC could have interfered with the summative mass closure calculations that were done to determine the total composition of the biomass.
  • Item
    Analysis of ore hand-crushed size distribution for grinding process in the artisanal and small-scale gold mines production: a case study of Nholi mine, Bahi district
    (College of Engineering and Technology, University of Dar es Salaam, 2022) Tembo, Malugu M.; Mdee, Ombeni J.
    In many parts of the world, artisanal and small-scale gold mines (ASGM) employed numbers of people compared to large-scale mines. The ASGM has been played a crucial role in poverty alleviation and rural development, particularly in developing countries. The mined ore is crushed and ground for beneficiation of gold. The grinding process involved the size reduction of blasted materials to acquire minerals of interest. This paper presents the size distribution of hand-crushed for blasted materials using sieve analysis and digital image processing. The sieve test results for hand-crushed blasted material of three muck-piles were ranged between 17 mm and 36 mm that is equivalent to 20% and 80% passings respectively, with an average of 26 mm. The digital image processing results were about 19.8 mm for 20% passing and 58 mm for 80% passing, with an average of 36.06 mm. The hand-crushed provided a wide range of material distribution than the required size in the grinding unit and increased oversize by 18%. The hand-crushed of blasted materials provides different sizes distribution leading to increase the residence time and power consumption of the grinding units.
  • Item
    Co-pyrolysis of cashew nut, coconut shells, and rice husk waste: kinetic and thermodynamic investigations
    (Tylor and Francis, 2022) Kazawadi, Deodatus; Ntalikwa, Justin; Kombe, Godlisten
    Co-pyrolysis of low ash content of coconut shell (CNS) and cashew nuts shells (CCS), and high ash content rice husk (RH) blends was performed using thermal gravimetric analysis (TGA). RH was blended with both CCS and CNS at 0, 30, 60, and 100% RH by mass. Results showed that CCS and CNS have low ash contents of 2.7 and 1.5%, respectively, while RH has high ash content of 26.7% on dry basis. TGA under nitrogen gas study was carried out at three heating rates of 10, 15, and 20 K/min. It was observed that the increase of CCS/CNS increased decomposition rates of blends. For example, RH increased from 6 to 7.7%/min when CNS was added. Furthermore, addition of low ash content leads to high decrease of maximum decomposition rates compared to high-high or low-low ash blends. Synergistic analysis has found out that a positive effect is observed when CNS/CCS is added to RH. The decrease of maximum decomposition temperature of 60–63°C compared to other studies of 10°C for all low and 40° for all high ashes is of great advantage. Flynn-Wall-Ozawa (FWO), Kissinger-Akahra-Sunose (KAS), and DAEM kinetic model analysis for 0.1 ≤α≤ 0.75 were used between 315 and 840°C. FWO model gave activation energy of 85, 70, and 75 kJ/mol, for RH, CNS, and CCS, respectively. Addition of low ash content biomass reduced activation energy of RH, activation energy of RH was reduced from 85 to 72 kJ/mol when CNS was added. RH requires high energy than the rest, example, RH needed 66.29 kJ/mol of energy compared to 51% of CNS and 56 kJ/mol for CCS. The entropy results were negative which implies a different orientation of molecules from origin samples properties. The Gibbs-free energies were positive and thus non-spontaneous process. Empirical models generated using SB model indicated that kinetics depends on reaction order and acceleration mechanism rather than diffusion and nuclei growth. Kinetically, the blending of high and low ash content biomass leads to high decrease of operating temperature and activation energy compared to low-low or high-high ash content blends. It has been recommended to further study on quality and quantity of product from such blends and the possibility of pre-treatment methods such as microwaves to improve pyrolysis of such blend