Chemical Engineering

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    A postal survey of effluent generation and disposal in the Zimbabwean dairy industry
    (Water research commision, 2002-04-02) Masiiwa, Husiel; Ikhu-Omoregbe, Daniel IO
    Water is a major utility in the dairy industry, which results in significant effluent volumes being generated, hence the challenge of its disposal cannot be ignored. In Zimbabwe, industry generally is not made to pay the full cost of managing industrial effluents, which inadvertently encourages environmental pollution. This paper presents the results of a postal survey of effluent generation and disposal by the dairy industry. A total of 30 questionnaires were sent out to various milk processors around the country out of which 15 were returned. The useful respondents receive and process 56% of the total milk produced in the country. The data obtained indicated that while some of the plants discharge their effluents into the municipal sewers, others discharge theirs by means of land irrigation. This latter method has the consequence of groundwater pollution. Respondents’ knowledge of effluent characteristics was generally low, which is not surprising as there are no stringent penalties for polluting.
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    Recovery of Lead from Lead Laden Cupels by a Simultaneous Leaching and Electrowinning Process in a Methanesulphonic acid bath
    (Sphinx Knowledge House, 2014) Mangunda, Cledwyn T.; Kuipa, Olga; Sithole, Tapuwa R.; Kuipa, Pardon K.
    Cupels are generated by mines during the fire assaying of precious group metals. The cupels contain lead which is a known environmental hazard hence the need to recover it. This work illustrates how leaching and electrowinning processes can be combined to produce a hybrid lead recovery process. Bench scale tests were conducted for the hybrid leaching and electro winning process using Methane Sulfonic Acid (MSA) as a leaching solvent at a concentration of 200g MSA per litre of water. A glass electrowinning cell fitted with a 9cm × 4cm pure lead cathode and 9cm × 4cm graphite anode with inter electrode gap of 15cm and a magnetic stirrer bar was used. Lead laden cupels (containing 30g lead) were subjected to simultaneous leaching and electrowinning and lead recovery after a period of 80 minutes was found to be 98%. The hybrid process was found to require about 20% less solvent than that required for the convectional leaching process which requires multiple stages to reduce the concentration of the solute in the raffinate to the same extent.
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    Imaging Ellipsometry Study on the effect of Electrolyte on the drainage of an Aqueous Film trapped between a Plane Hydrophilic Silica Surface and an approaching Organic droplet
    (Sadguru publications, 2014) Kuipa, Olga; Kuipa, Pardon K.
    An imaging ellipsometer is used to study the drainage of an aqueous film trapped between a hydrophilic silica equilateral prism surface and a heptane or butylacetate droplet. The interfacial droplet profile on approach to the hydrophilic silica surface is such that the droplet is dimpled at its center with the periphery of the droplet (the barrier ring) being the region of closest approach to the hydrophilic silica surface. The time it takes for these drops to either achieve an equilibrium film thickness at the barrier ring or to coalesce with the macroscopic hydrophilic silica surface was experimentally determined; drainage time increases whilst equilibrium film thickness decreases with increasing salt concentration in the continuous phase. The increase in drainage time is attributed to hindered drainage of the aqueous film due probably to an increase in the aqueous film viscosity, which should translate into a decrease in the film elasticity. Compression of the double layer may also qualitatively explain the observed decrease in equilibrium film thickness at the barrier ring as the salt concentration increases. When aluminum chloride is used as the electrolyte the equilibrium film thickness is relatively constant (around 90 ± 10 nm) for the range of concentrations studied. This may be due to the fact that the aluminum ion has a valence of three and may screen electrostatic interactions between the oil droplet and the hydrophilic silica surface at relatively lower aluminum chloride concentrations.
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    Removal of Cr(VI) from Aqueous Solutions Using Powder of Potato Peelings as a Low Cost Sorbent
    (Hindawi Publishing Corporation, 2014-06) Mutongo, F.; Kuipa, Olga; Kuipa, Pardon K.
    Potato peels which are a low cost, renewable agroindustry by-product were used for the removal of hexavalent chromium from aqueous effluents. Batch experiments were carried out with an artificial effluent comprising of potassium dichromate in deionised water. The effects of the initial hexavalent chromium concentration, dose of biosorbent, and removal kinetics were explored. An adsorbent dosage of 4 g/L was effective in complete removal of the metal ion, at pH 2.5, in 48 minutes. The kinetic process of Cr(VI) adsorption onto potato peel powder was tested by applying pseudo-first-order and pseudo-second-order models as well as the Elovich kinetic equation to correlate the experimental data and to determine the kinetic parameters. The adsorption data were correlated by the Langmuir and Freundlich isotherms. A maximum monolayer adsorption capacity of 3.28 mg/g was calculated using the Langmuir adsorption isotherm, suggesting a functional group limited adsorption process. The results confirmed that potato peels are an effective biosorbent for the removal of hexavalent chromium from effluent.
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    Treatment of Low Turbidity Water Using Poly-Aluminium Chloride (PAC) and Recycled Sludge: Case study Chinhoyi
    (Zimbabwe Journal of Science & Technology, 2015) Jowa, Taurai; Mguni, Liberty L
    Coagulation of low turbidity water using PAC and recycled sludge was studied using a bench scale sedimentation jar test operated at ambient temperature and pressure. Tests were done on low turbidity raw water samples from the river Manyame in Chinhoyi. The coagulants tested were aluminium sulphate (control), PAC and recycled sludge. The effects of the coagulants on the final physical properties of treated water (pH, conductivity, floc quality and most importantly turbidity) were analysed. It was observed that for 60 mg/L dosages, final pH was in the 8.2-8.4 range with an average of 0.24 unit change for PAC and 0.12 for aluminium sulphate, changes in conductivity were less than 20 μScm-1for both coagulants and PAC was more efficient in turbidity removal at all dosages. The higher efficiencies of PAC where due to the poly-ions formed during hydrolysis. An improvement to the coagulating system was attempted by using settled sludge from clarifiers. At a constant 30 mg/L PAC dosage, the maximum turbidity removal efficiency, 73%, was observed at 6 ml sludge dosage.
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    Removal of Pyrethrin from Aqueous Effluents by Adsorptive Micellar Flocculation
    (Hindawi Publishing Corporation, 2015-01-06) Kuipa, Olga; Kuipa, Pardon K.
    The equilibrium adsorption of pyrethrin onto aggregates formed by the flocculation of micelles of the surfactant sodium dodecyl sulphate (SDS) with aluminium sulphate is reported.The experimental results were analysed using different adsorption isotherms (Langmuir, Freundlich, Redlich-Peterson, Sips, Radke-Prausnitz, Temkin, linear equilibrium, and the Dubin-Radushkevich isotherms). The Freundlich and linear equilibrium isotherms best describe the adsorption of pyrethrin onto SDS micellar flocs, with the Freundlich adsorption constant, 𝐾 𝐹, and the mass distribution coefficient, 𝐾 𝐷, of 64.266 ((mg/g)(L/mg)1/𝑛) and 119.65 L/g, respectively. Applicability of the Freundlich adsorption model suggests that heterogeneous surface adsorption affects the adsorption. The mean free energy value estimated using the Dubinin-Radushkevich isotherm was 0.136 kJ/mol indicating that physisorption may be predominant in the adsorption process.
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    Beverage Effluent Treatment Technology
    (2016) Tshuma. J.; Maqhuzu, A.; Bhebhe, S.; Mudon, S.; Kaitano, H.; Mashanga, D.; Mpofu, C.; Tshuma, I.; Mkandla, C.K.
    A detailed beverage effluent treatment technology was developed in a period of 4 months, using samples from an operating beverage plant. The total number of samples collected were 1304. The volume of the sample collected hourly was 500ml for 4 hours to give a composite sample. The plant operated continuously for 6 days a week and had two-12 hour shifts a day. The technology consisted of four water treatment methods combined consecutively which were chemical, physical, biological and physical treatment methods. The aim of developing the technology was to reduce the sCOD, TSS and pH parameters to the required environmental specification. The untreated beverage wastewater has high solids content, high organic matter, and low pH which need pretreatment before it is discharged into the municipal sewage treatment works. The developed technology reduced the high solid content, high organic load and adjusted the pH to the required Bulawayo Municipality environmental specifications. The average percentage reduction in sCOD and TSS was 91.1% and 90.6% respectively. The pH was adjusted to 8.05. The obtained results indicated that the developed technology was effective for treating beverage wastewater at ambient temperature to meet the quality of effluent that can be discharged into public water works.
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    Processing Of Gold-Bearing Sand,Dumps: A Case Study In Zimbabwe
    (CISA, 2017-10) Hlabangana, N.; Bhondayi, C.; Mguni, N. G; Hildebrandt, D.; Danha, Gwiranai
    In this article, we investigate the possibility of reprocessing gold bearing gold dumps for gold as a sustainable way of reviving the mining sector in Zimbabwe. Heap or vat leaching is a process that has been extensively used for the recovery of valuable metals like copper, gold (Au) and silver. The ore is prepared for vat leaching by either crushing or milling it into fine and deslimed material. It is then placed into a container (vat), which has a partial filter floor. Cyanide solution can then be injected either through the filter section of the floor or added to the top of the ore charge.
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    Determining Optimum Wet Milling and Leaching Parameters for Maximum Recovery of Gold
    (Research Publish Journals, 2017-12) Mguni, Nonhlanhla G.; Bhebhe, Siboniwe; Danha, Gwiranai; Tshuma, Joel; Hlabangana, N.
    Abstract: The comminution and leaching unit operations play a vital role in the extraction process of valuable minerals from ores. Historical research efforts have focused more on optimizing these two unit operations individually rather than as an entire integrated process. The approach employed in modern day research is now driven by the process intensification philosophy. Process intensification detects that developing an integrated approach to mineral processing systems and flow sheets leads to improved efficiency of the overall process and can help attain optimum recovery and a reduction in energy and material costs. In this article, we present laboratory scale batch grinding and leaching profiles of a mono-sized gold ore sample (-1700 + 850 μm). The sample was obtained from a run-of-mine (ROM) ore of one the leading gold processing plants in South Africa. Various combinations of grinding media fill level and ball size were investigated, showing that breakage is more pronounced for the larger ball sizes tested. We also found that using a higher media filling (J = 30%) and a larger media size (30 mm) consumed more energy with less gold recovered during a 24 hour leaching period, compared to when a smaller J of 15% and 20 mm media was used. Our results show that efficient application of energy is vital and maximum profit is a complex function of energy usage and particle size. Keywords: gold, Historical research, mineral processing, energy, material costs.
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    Determining an optimal interstitial filling condition: An Attainable Region approach
    (Elsevier, 2018) Hlabangana, N.; Madiba, M.S.; Bhondayi, C.; Mguni, Nonhlanhla G.; Danha, Gwiranai
    In this article, we present yet another application of the Attainable Region (AR) method to data from a laboratory scale milling of a low grade gold ore. In this particular case, we investigate how to optimize the amount of material in a desired size class for a scenario where the boundaries of the desired size class of interest are changed. The AR approach has never been applied in such a scenario before. Using a mono sized feed of − 1700 + 850 μm, two desired product size classes of interest (− 850 + 150 μm and − 150 + 75 μm) are selected in order to determine the optimum interstitial filling (U) to be used in the mill. Two different values of U, 1.75 and 1.0 respectively, are obtained as optimal. Our results also show that optimal operating conditions are different for different objective functions. We demonstrate that the AR may be used to specify optimal conditions that may be used for particle size reduction processes. We also illustrate how an AR boundary for optimization purposes can in certain cases be extended using the ‘mixing principle’.
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    Effect of ball and feed particle size distribution on the milling efficiency of a ball mill: An attainable region approach
    (2018) Hlabangana, N.; Danha, G.; Muzenda, E.
    In this article, alternative forms of optimizing the milling efficiency of a laboratory scale ball mill by varying the grinding media size distribution and the feed material particle size distribution were investigated. Silica ore was used as the test material. The experimental parameters that were kept constant in this investigation was the grinding media filling, powder filling and the mill rotational speed. The data obtained from these batch tests was then analyzed using a model free technique called the Attainable Region method. This analysis technique showed that the required product fineness is a function of grinding media and feed material size distributions. It was also observed from the experimental results that in order to increase the milling efficiency of a ball mill, towards optimum production of material in the desired size class, there is a need to correlate the ball size and the feed size distributions.
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    Effect of frother and depressant interaction on flotation of Great Dyke PGM ore.
    (The Southern African Institute of Mining and Metallurgy., 2018-01) Mberi, T.; Mguni, Liberty.L; Ntuli, Freeman
    In the optimization of platinum group metal flotation plants, various parameters are considered in order to achieve the desired recovery and grade of the precious metals. There should be a balance in the operating parameters so as to produce a high-grade valuable mineral concentrate without compromising recovery. This project seeks to investigate the individual and interactive effect of flotation reagents at different dosages, using a full factorial experimental design approach with two factors at six levels. Laboratory tests were conducted to illustrate the effect of frother and depressant on flotation. The results were analysed using SPSS and MiniTab. Based on the F-test at 95% confidence level, the frother had no significant effect on the concentrate grade but had a significant effect on 4E recovery, mass pull, and water recovery. The depressant had a significant effect on concentrate grade, water recovery, and mass pull. The interactive effect of frother and depressant had significant negative effect on all responses except concentrate grade. The optimum levels for recovery and grade were analysed assuming equal importance of grade and recovery as well as double importance for grade.
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    Effect of ball and feed particle size distribution on the milling efficiency of a ball mill: An attainable region approach
    (Elsevier, 2018-02-09) Hlabangana, N.; Danha, Gwiranai; Muzenda, E
    In this article, alternative forms of optimizing the milling efficiency of a laboratory scale ball mill by varying the grinding media size distribution and the feed material particle size distribution were investigated. Silica ore was used as the test material. The experimental parameters that were kept constant in this investigation was the grinding media filling, powder filling and the mill rotational speed. The data obtained from these batch tests was then analyzed using a model free technique called the Attainable Region method. This analysis technique showed that the required product fineness is a function of grinding media and feed material size distributions. It was also observed from the experimental results that in order to increase the milling efficiency of a ball mill, towards optimum production of material in the desired size class, there is a need to correlate the ball size and the feed size distributions
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    Optimisation of the Leaching Parameters of a Gold Ore in Sodium Cyanide Solution
    (2018-03) Hlabangana, N.; Bhebhe, Siboniwe; Mguni, Nonhlanhla G.; Danha, Gwiranai; Tshuma, Joel
    The objective of the work reported in this paper is to propose ways of improving the recovery on a low grade gold ore. To date, no work on optimizing this particular ore has been done in order to improve the recovery. Five size fractions used in the leaching tests reveal that recovery is a function of operational parameters. The optimum values for these parameters that gave a maximum recovery were: particle size (-150 + 75 μm) concentration of the lixiviant (210 ppm), temperature (85oC) and mixing speed (900 rpm). We then applied the shrinking core model and ash layer diffusion is the slowest step. An empirical model was then proposed to predict the leaching behaviour of the gold ore. A value of 12, 9 kJ /mol was obtained for Activation Energy (Ea) which is consistent with some results from leading researchers.
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    Extraction of magnesium from chrome slag by sulphiric acid leaching at low temperatures
    (Novateur, 2018-11) Dube, Samukeliso; Tshuma, Bret; Jele, Thabisile B; Nkompilo, Sikhulile; Tshuma, Lawrencia; Moyo, Langa B; Hlabangana, Nkosikhona; Nkomo, Fortune; Ncube, Phendukani
    In this this article ,a solvent extraction method by using sulphuric acid leaching was developed .The process conditions and parameters of sulphuric acid concentration ,leaching temperature ,leaching time and solid to liquid ratio were studied. These studied conditions and parameters were varied from 0.5M to 5M at 0.5 M interval, 30oC to 60oC at 5oC interval and 30 minutes to 240 minutes at 30 minute interval respectively. The solid to liquid ratios used were 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10.The optimum percentage extraction efficiency of magnesium as found to be 66.87% at optimum operating conditions of 4M sulphuric acid concentration 60oC leaching temperature, 120 minutes leaching time and 1:2 solid to liquid ratio.
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    Investigating the feasibility of using agricultural waste as an adsorbent of gold ions in small scale gold processing plants.
    (2019) Tapfuma, A.; Chakawa, D.P.; Moyo, L.B.; Hlabangana, N.;; Danha, G.; Muzenda, E.
    The recovery of precious metals like gold is increasing each day due to its high market prices along with diverse applications. Bio-sorption represents a biotechnological innovation as well as a cost effective and excellent tool for recovery of precious metals from aqueous solutions. This study offers an overview of a recent scenario of bio-sorption studies carried out on the use of some promising bio-sorbents which could serve as an economical means for recovering gold for small scale gold processing plants. Results show that activated carbon (control) has the highest adsorption efficiency since it contains more active site on the carbon molecules. The activated maize corn cob had the highest adsorption efficiency (77.09%) compared to all other agricultural adsorbents. Banana peels showed a significant adsorption efficiency of 56.87%.
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    The effect of a sulphate-reducing bacteria on the rate of corrosion of steel alloys
    (2019) L. Shakua, L.; G. Danha, G.; Hlabanganac, N.; Bhero, S.
    three analytical techniques we will employ in measuring the rate of corrosion are the electrochemical impedance spectroscopy, cyclic polarization and the mass loss method. The test material used is the 316L stainless steel and the mild steel coupons. The microorganism we are going to use for this investigation is the sulphate-reducing bacteria (SRB). The scope of the study will cover the cultivation of the micro-organism, cell count, electrochemical testing, cyclic polarization testing, analysis of corrosion product, mass loss and the pitting morphology consistent with the microbiologically induced corrosion mechanism. Our results show that the chemical composition of the mild steel and stainless steel test material conformed to SAE1020 and Type 316L stainless steel respectively. We also found that the corrosion rate of mild steel in both biotic and abiotic systems was significantly higher than that of the 316L stainless steel. The biotic system was more corrosive for both the mild steel and the 316L stainless steel. The biotic system showed a substantial corrosion effect in two days while the abiotic system showed the same effect after seven days. The cell count procedure confirmed the presence of sulphate-reducing bacteria throughout the test. Keywords: Type your keywords here, separated by semicolons ; Available online at www.sciencedirect.com ScienceDirect Procedia Manufacturing 00 (2019) 000–000 www.elsevier.com/locate/procedia 2351-9789 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of SMPM 2019. *Corresponding Author Email: danhag@biust.ac.bw 2nd International Conference on Sustainable Materials Processing and Manufacturing (SMPM 2019) The effect of a sulphate-reducing bacteria on the rate of corrosion of steel alloys L. Shakua , G. Danha*b , N. Hlabanganac , S. Bherob a Department of Metallurgy, P.O Box 16, Johannesburg, South Africa b Department of Chemical Engineering, National University of Science & Technology, Box A.C 939 Ascot, Bulawayo, Zimbabwe c Department of Chemical, Materials and Metallurgical Engineering, Faculty of Engineering and Technology, Botswana International University of Science and Technology, Plot 10071 Boseja Ward, Private Bag 16 Palapye, Botswana Abstract In this article, we investigate the effect of micro-organisms on the rate of corrosion of stainless steel and mild steel alloys. The three analytical techniques we will employ in measuring the rate of corrosion are the electrochemical impedance spectroscopy, cyclic polarization and the mass loss method. The test material used is the 316L stainless steel and the mild steel coupons. The microorganism we are going to use for this investigation is the sulphate-reducing bacteria (SRB). The scope of the study will cover the cultivation of the micro-organism, cell count, electrochemical testing, cyclic polarization testing, analysis of corrosion product, mass loss and the pitting morphology consistent with the microbiologically induced corrosion mechanism. Our results show that the chemical composition of the mild steel and stainless steel test material conformed to SAE1020 and Type 316L stainless steel respectively. We also found that the corrosion rate of mild steel in both biotic and abiotic systems was significantly higher than that of the 316L stainless steel. The biotic system was more corrosive for both the mild steel and
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    An attainable region approach for the recovery of iron and zinc from electric arc furnace dust
    (2019) M.C. Siamea, M. C.; Kaomab, J.; Hlabanganac, N; Danhad, G.
    This study investigated the application of the attainable region optimization technique to establish the optimum hybrid hydrometallurgical and pyro-metallurgical process conditions required to treat the electric arc furnace dust. The analysis of the results obtained showed that a combination of an agitation speed of 800 rpm, sodium hydroxide concentration of 8.0 mol/L and a leaching temperature of 80 °C were the optimum conditions for the hydrometallurgical process, while a roasting temperature of 1200 °C, carbon content of 35.27% and a roasting period of 36 h were the optimum conditions for the pyro-metallurgical process. The iron recovered from the dust was recycled in order to upgrade the iron content of the electric arc furnace charge, thereby reducing both process loses and process wastes.
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    An attainable region approach for the recovery of iron and zinc from electric arc furnace dust
    (2019) Siame, M.C.; Kaoma, J.; Hlabangana, N.; Danha, G.
    This study investigated the application of the attainable region optimization technique to establish the optimum hybrid hydrometallurgical and pyro-metallurgical process conditions required to treat the electric arc furnace dust. The analysis of the results obtained showed that a combination of an agitation speed of 800 rpm, sodium hydroxide concentration of 8.0 mol/L and a leaching temperature of 80 °C were the optimum conditions for the hydrometallurgical process, while a roasting temperature of 1200 °C, carbon content of 35.27% and a roasting period of 36 h were the optimum conditions for the pyro-metallurgical process. The iron recovered from the dust was recycled in order to upgrade the iron content of the electric arc furnace charge, thereby reducing both process loses and process wastes.
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    Optimization of pulp production from groundnut shells using chemical pulping at low temperatures
    (2020) Musekiwa, P.; Moyo, L.B.; Mamvura, T.A.; Danha, G.; Simate, G.S.; Hlabangana, N.
    Paper production through chemical pulping has been identified as one of the ideal avenues of exploring the uses of groundnut shells as they are rich in cellulose. Ideally, the cellulose can be used to synthesize fibres that can be converted into useful paper products. In this study, chemical pulping was the chosen process for liberating the fibres as it is effective in dissolving lignin embedded within the cellulose. In addition, the fibres produced have superior physical properties compared to mechanical pulping. It is imperative that optimal conditions are identified for the chemical treatment process, in order to ensure that energy and chemical consumption are minimized. All these measures are aimed at reducing production costs and make chemical pulping economically viable, as compared to the mechanical pulping process which is less costly. Response surface methodology (RSM) was used in this study to evaluate the effect of three independent variables (cooking time, temperature, and sulphidity) on pulp yield and kappa number. These parameters are critical in the chemical pulping process and the optimal conditions obtained were 180 min, 100 C and 23.6 wt.%, respectively. At the optimal conditions, the pulp yield was 64.39wt% with a kappa number of 19.5. The results showed that all parameters investigated, had a statistically significant effect on the production of pulp. The increased cooking time was efficient in ensuring complete impregnation of the groundnut shells with chemicals for pulping and ensuring that the dissolution of lignin is not selective and does not result in dead spots inherently compromising the quality of the pulp. On the other hand, lower temperatures limited the peeling effect due to hydrolysis of carbohydrates which increased pulp yield due to a higher cellulose retention. Consequently, this contributed towards obtaining pulp that is well cooked, has a low bleach consumption and a higher quality.