Chemical Engineering

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Adsorption of Mercury by Pterocarpus Anglolensis: Study on Adsorption Isotherms and Kinetics
(Iranian Institute of Research and Development in Chemical Industries (IRDCI)-ACECR, 2022) Mapombere, Garainesu; Nyoni, Bothwell; Sibali, Linda L.; Chiririwa, Haleden; Seodigeng, Tumisang
The efficiency of Pterocarpus Anglolensis sawdust, an abundantly available waste product of the timber industry, capacity as an adsorbent for mercury was investigated. A series of batch experiments was carried out with experimental conditions of metal concentration, adsorbent concentration, pH, and contact time being changed. The concentration of the metal ion was deduced using spectrophotometric means. The adsorption efficiency was found to be pH-dependent with pH 4 being the optimum. 90 minutes was found to be the equilibrium time with particle size range 90-124 μm being the most efficient. Maximum adsorption of mercury was evaluated at 80.33 %. The experimental data was best modeled by the Freundlich isotherm and Pseudo second-order kinetic models. The calculated adsorption parameters are Kf = 0.0002 L/mg, bF = 3.0 and k2 = 0.00016 g/μg.min.
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.
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.
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.
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’.
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.
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
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.
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.
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.
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.
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%.
On the efficacy of a proposed unsteady state heat loading protocol
(NetJournals, 2020) Bepete, S.; Dlodlo, T.S.; Mudono, S.; Marwizi, T.
The paper relates to the thermodynamics of heat transfer processes in which the source of heat is a hot gaseous fluid. The effect of systematically introducing alternating conditions of compression and decompression inside a heat exchanger is investigated. The said alternating conditions are actuated by introducing two periodic valves at the heat exchanger inlet and outlet. This unsteady state mode of operation is shown to result in enhanced heat exchange under certain conditions. This method of heat exchange has been termed ‘Unsteady State Heat Loading Protocol (USHLP).’ Experiments were carried out to compare steady state and USHLP based heat transfer in the context of steam providing heat to a water evaporation process. In the experiments, heat was transferred from steam to an evaporation process through a jacket type heat exchanger. An increase in efficiency of around 42% was observed from replacing steady state heat transfer with USHLP under the same operating conditions and geometric configuration. The results of the experiments are discussed in the concluding sections of the paper. It was noted that consistently less steam was used per unit amount of water evaporated in experiments where USHLP was used as compared to steady state heat transfer
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.
Optimisation of using a blend of plant based natural and synthetic coagulants for water treatment: ( Moringa Oleifera-Cactus Opuntia-Alum Blend)
(2020) Gandiwa, B.I.; Moyo, L.B.; Ncube, S.; Mamvura, T.A.; Hlabangana, N.
The research presents a comparative study on the effectiveness of blending plant based natural coagulants (Cactus Opuntia and Moringa Oleifera extracts) and a synthetic coagulant (aluminium sulphate or alum) in treatment of raw water. The low production rates of natural coagulants has derailed their commercialization this has driven the idea of blending synthetic coagulants which is envisaged to be the more appropriate means of application in this study. To measure the effectiveness of the coagulant, the following parameters were measured; turbidity, pH, conductivity and total alkalinity. The simplex lattice experimental design was applied using Minitab Software to obtain the optimal coagulant blend. The models were validated by statistical analysis which showed that the model was sufficient and no further modeling was required. The optimization results showed that a combination of alum, Moringa Oleifera and Cactus Opuntia in proportions of 13%, 42.6% and 44.4%, respectively with a total coagulant dosage of 45mg/L gave the best overall results with the resultant water having a turbidity, pH, conductivity and total alkalinity of 2.7 NTU, 6.99, 308 µS/cm and 137.7mg/L respectively. These physiochemical parameters are within required limits for potable water as per WHO guidelines. From the results, it was concluded that aluminum sulphate (alum) can be successfully blended with natural plantbased coagulants for raw water treatment.
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.
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.
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.
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.
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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