Establishment of background radiation dose rate in the vicinity of the proposed Manyoni Uranium Project, Singida

The absorbed dose rate in air in the vicinity of the proposed Manyoni uranium mining project located in Singida region, Tanzania, was determined so as to establish the baseline data for background radiation dose rate data prior to commencement of uranium mining activities. Twenty stations in seven villages were selected and monitored for six months from June 2012 to November 2012. The absorbed dose rate in air was measured by means of CaF2:Dy thermoluminescent dosimeters (TLD-200). The annual effective dose was estimated using outdoor occupancy factor of 0.2 and conversion coefficient factor of 0.7 SvG y-1. The mean dose rate was found to range from 16.68 - 507.00 nGy h-1 with an average of 74.86 nGy h-1. Maximum average dose rate of 396.7 nGy h-1 was found at station number 8 situated in Mwanzi Village which was about 7 times higher than the world average value of 59 nGy h-1 (UNSCEAR 2008) corresponding to annual effective dose of 0.5mSv y-1. This value is 2 fold lower than the recommended limit of 1 mSv y-1 for a member of the public (ICRP 1990). Minimum avarage dose rates of 30.9 nGy h-1 was found in station number 16 and 17 located in Aghondi village, corresponding to annual effective dose of 0.04 mSv y-1. This implies that prior to commencement of uranium mining activities in the proposed area the external exposure rates due to the natural background radiation are lower than the world recommended value.Keywords: Absorbed dose rate, Uranium mining, Background radiation, Thermoluminescent dosimeter, Annual effective dos

Capacitive deionization: a promising technology for water defluoridation: a review

This research article was published by IWA publishing, Volume 22, No. 1, 2021Capacitive deionization (CDI) is among the promising technologies employed for water purification. CDI has been studied for the removal of various ionic species from water including fluoride ion (F ) with promising results. However, there is no comprehensive literature that sum marizes the use of CDI for water defluoridation applications. Therefore, this review paper critically analyzes different electrode materials that have been studied for water defluoridation, their electrosorption capacities and F removal efficiencies. It further discussed the parameters that influence CDI efficiency during defluoridation and point out the issues of F selectivity when co-existing with other ions in the solution. We can conclude that different electrode materials have shown different abilities in electrosorption of F . The carbon-based materials pos sess high surface area and good electrical conductivity which is paramount for ion adsorption but gives lack selectivity for F removal. Metal oxides and hydroxides have been reported with improved electrosorption capacity and high selectivity to F due to the ion exchange between the F and the hydroxyls surface of the metal oxides/hydroxides. Apart from the good performance of these materials for defluor idation, the discovery of actual practical use of the electrode materials for defluoridation for commercial scal

Capacitive Deionization for the Removal of Paraquat Herbicide from Aqueous Solution

This research article was published by Hindawi, 2021In comparison to other conventional methods like adsorption and reverse osmosis (RO), capacitive deionization (CDI) has only been investigated extensively for the removal of inorganic pollutants from water, demonstrating limited practicality. Herein, the study investigated the use of CDI for the removal of paraquat (PQ) herbicide from water by using commercial activated carbon (AC) electrodes. The CDI performance was examined as a function of the initial PQ concentration, applied voltage, flowrate, treatment time, and cycle stability testing in the batch mode approach. The applied voltage had a beneficial effect on the removal efficiency, whereas the removal efficiency of PQ declined as the initial PQ concentration increased. However, the electrosorption capacity gradually increased with the increase of initial feed solutions’ concentration. The maximum removal efficiency and electrosorption capacity achieved at 5 mg/L and 20 mg/L PQ initial concentrations, an applied voltage of 1.2 V, and 5 mL/min flowrate were 100% and 0.33 mg/g and 52.5% and 0.7 mg/g, respectively. Washing the electrodes with distilled water achieved sequential desorption of PQ, and the process produces a waste stream that can be disposed of or treated further. Therefore, the CDI method is considered a promising and efficient method for removing organic pollutants from water including pesticides

Modification strategies to enhance electrosorption performance of activated carbon electrodes for capacitive deionization applications

This research article published by Elsevier, 2019Capacitive deionization (CDI) is the competitive technology for water desalination which appears to become an alternative to conventional methods such as ion exchange resins, reverse osmosis, and electrodeionization. Variety of materials including, carbide-derived carbon, activated carbons, carbon nanotubes, carbon aerogels and mesoporous carbons have been studied for CDI applications most of them being porous carbons. However, materials such as carbon nanotubes are highly expensive and hinder applications at large industrial scale. Activated carbon is a cheap and commercially available electrode material for CDI though its desalination capacity is limited by factors such as low electrical conductivity, inability to selectively remove specific ions, co-ion expulsion, poor wettability, inappropriate pore size distribution and lack of inter-pore connectivity to enable ion diffusion. These factors have raised a concern to most researchers and try to find a way to modify the surface of porous materials. Some strategies have been used to modify activated carbons including dip-coating in dopamine solution, mixing with quaternized poly (4-vinylpyridine), combining with graphenes and carbon nanotubes, direct fluorination and etching in acid solution to mention few. This review highlight factor(s) that cause low performance of activated carbon and modification strategies used to treat activated carbon to enhance its adsorption performance. Furthermore, characterization methods used to confirm whether the modification was successful and the practical application of modification methods have been discussed. To our view this work will provide an understanding of the contribution offered by modified activated carbon electrodes in the development of CDI technology

Porous carbon derived from Artocarpus heterophyllus peels for capacitive deionization electrodes

This research article published by Elsevier Ltd., 2019Sustainable clean water for human use can be attained through cost effective water purification technologies where by capacitive deionization (CDI) technology is among them. To attain high CDI performance porous carbon materials with good electrical conductivity, high surface area, specific capacitance and good chemical stability are essential. In this study high surface area porous carbon has been synthesized through carbonization of agricultural waste jackfruit peels (Artocarpus heterophyllus) followed by KOH activation at 600, 700, and 800 °C for 1 h. It was found that, the activation temperature significantly increased the BET surface area of the synthesized carbon from 607 m2/g to 1955 m2/g. Desalination experiments were carried out with 30–500 mg/L NaCl solution in batch mode at a flow rate of 2.5 ml/min while applying voltage of 1.2, 1.4 and 2.0 V to the cell. The electrosorption capacity and salt-removal efficiency increased with increasing BET Surface area and applied potential. Specifically, ACJF1:1-700 exhibited highest specific capacitance of 307 F/g, high salt removal efficiency and electrosorption capacity of 5.74 mg/g when voltage of 2 V was applied. These results indicated that the Artocarpus heterophyllus can be promising CDI electrode materials for low salinity water desalination

Water defluoridation using Al/Fe/Ti ternary metal oxide-loaded activated carbon by capacitive deionization

This research article was published by Royal Society of Chemistry, 2023Capacitive deionization (CDI) is an environmentally friendly water treatment technology with low energy consumption. For a long time, activated carbon has been a preferred electrode material for CDI owing to its availability, easy preparation, low cost, and tunable textural properties. However, an unmodified carbon electrode does not significantly prefer anions, leading to unnecessary energy consumption for treating fluoridated water. Therefore, in this study, activated carbon materials loaded with trimetallic oxides (Al/Fe/Ti) at different mass ratios were prepared by a co-precipitation method in a temperature range between 23 and 27 °C to improve fluoride ion (F−) selectivity. The as-prepared composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy analysis. The process parameters were investigated and optimized based on experimental data using the response surface methodology (Box–Behnken design). In competitive F− removal CDI experiments, the F− concentration was reduced from 5.15 mg L−1 to 1.18 mg L−1, below the allowable limit of 1.5 mg L−1 set by the World Health Organization. The metal oxide-modified activated carbon surface (AC–Al4Fe2.5Ti4) showed significantly improved electrochemical properties and enhanced capacitance compared to the unmodified one. The modified electrode material also showed the advantages of high removal efficiency and excellent regeneration performance after continuous electric adsorption–desorption cycles. Therefore, activated carbon–Al4Fe2.5Ti4 is a potential CDI electrode material for water defluoridation applications

Highly porous biomass-based capacitive deionization electrodes for water defluoridation

This research article published by Springer Nature Switzerland AG., 2019The high concentration of fluoride (F−) in water sources is the main challenge in major fluoride belts. Though capacitive deionization (CDI) with porous carbon electrodes is the promising alternative in removing charged species from aqueous solution, little has been presented on the usefulness of CDI with biomass-based electrodes in removing F− from natural water existing together with other ions such as Ca2+ and Mg2+. This study investigated the feasibility of using biomass-based electrodes for natural water defluoridation application. Porous carbon was synthesized from jackfruit peels (JFAC) through potassium hydroxide (KOH) activation. Surface morphology, pore structure, and electrochemical properties of the JFAC were investigated. The textural properties of the synthesized carbon and electrochemical characteristics of the fabricated electrodes were found to be influenced by activation temperature. Brunauer-Emmett-Teller (BET) surface area, pore diameter, pore volume, and pore surface area increased with an increase in activation temperature and KOH to carbon ratio. It was further confirmed that as the applied voltage increased from 1.2 to 2 V, the amount of adsorbed anions increased without significantly affecting the pH of the water. At 2.0 V, the electrodes showed a maximum F− adsorption efficiency and electrosorption capacity of 62% and 0.13 mg/g respectively. The electrosorption capacity depends on the initial concentration of the ion in the feed water. It was further observed that natural organic substances contained in the natural water might inhibit JFAC electrode surface and decrease its adsorption efficiency. This study provides cost-effective CDI electrode material prepared from biomass for water defluoridation

Biomass-based carbon electrode materials for capacitive deionization: a review

This research article published by Springer Nature Switzerland AG., 2019Capacitive deionization (CDI) is a promising water purification technology which works by removing salt ions or charged species from aqueous solutions. Currently, most of the research on CDI focuses on the desalination of water with low or moderate salt concentration due to the low salt adsorption capacity of the electrodes. The electrosorption capacity of CDI relies on the structural and textural characteristics of the electrode materials. The cost of electrode materials, the complicated synthesis methods, and the environmental concerns arising from material synthesis steps hinder the development of large-scale CDI units. By considering the good electrical conductivity, high specific surface area (SSA), porous structure, availability, mass production, and cost, porous carbon derived from biomass materials may be a promising CDI electrode material. This review presents an update on carbon nanomaterials derived from various biomasses for CDI electrodes. It covers different synthesis methods and the electrosorption performance of each material and discusses the impact of the SSA and porous structure of the materials on desalination. This review shows that a variety of biomass materials can be used to synthesize cost-effective CDI electrode materials with different structures and good desalination performance. It also shows that diverse precursors and synthesis routes have significant influences on the properties and performance of the resulting carbon electrodes. Additionally, the performance of CDI does not depend only on BET surface area and pore structure but also on the applied voltage, initial concentration of the feed solution, and mass, as well as the capacitance of the electrodes

Adsorption-capacitive deionization hybrid system with activated carbon of modified potential of zero charge

This research article was published by Elsevier, 2023In this study water solutions are desalinated with carbon electrodes of modified surface charges. The idea is to endow the electrodes with the ability to physically adsorb salt ions without applying potential so as to save energy. The modification enhanced to decrease the energy consumption of a newly invented adsorption-CDI hybrid system by 19%, since modified activated carbon cell consumed 0.620 (relative error 3.00%) kWh/m3 compared to pristine activated carbon cell which consumed 0.746 (relative error 1.20%) kWh/m3. Further analysis revealed high adsorption capacity of the modified activated carbon electrode cell which exhibited 9.0 (relative error 2.22%) compared to activated carbon cell with 5.3 (relative error 5.66%) mg g−1. These results show the potential of surface modification in adding value to low cost activated carbons for application in CDI

Mesoporous carbon materials derived from artocarpus heterophyllus for water desalination and defluoridation using capacitive deionization

A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Sustainable Energy Science and Engineering of the Nelson Mandela African Institution of Science and TechnologySustainable clean water for human use can be attained through cost-effective water purification technologies whereby capacitive deionization (CDI) technology is among them. To attain high CDI performance porous carbon materials with high surface area, specific capacitance, and good chemical stability are essential. In this study, high surface area mesoporous carbon has been synthesized from jackfruit peels (Artocarpus heterophyllus) through chemical activation method. Two different activation routes were used; carbonization followed by KOH activation and direct activation with H 3 PO 4 . In KOH activation route, the activation process was done by varying activation temperature from 600 to 800 ˚C and KOH to carbon ratio (KOH/C) from 1 to 3 for 1 h. In H 3 PO 4 route, activation was done by varying concentration of H 3 PO 4 from 10 to 35% and activation temperature from 450 to 550 ˚C for 1 h. The textural properties of the synthesized jackfruit activated carbon (JFAC) and electrochemical characteristics of the fabricated electrodes were found to be influenced by activating agent ratio/concentration and activation temperature. The synthesized JFAC possess a honey comb-like structure with plentiful mesopores at a pore size range of 3.0-5.0 nm which are beneficial for electrosorption. The BET surface area and pore volume of the carbonized jackfruit peels (JFC) increased from 607 to 2681 m 2 /g and 0.52 to 2.61 cm 3 /g respectively, upon activation with KOH/C ratio of 2 at 800 °C. Nitrogen adsorptiondesorption studies revealed that the synthesized JFAC is mainly mesopores characterized by type IV isotherms according to IUPAC classification. Desalination experiments were carried out with 30 to 500 mg/L NaCl solution in batch mode at a flow rate of 2.5 mL/min while applying a voltage of 1.2, 1.4 and 2.0 V to the cell. The electrosorption capacity and saltremoval efficiency increased with increasing BET surface area and applied potential. Among the samples studied, carbon produced with KOH/C ratio of 1 at 700 ˚C (JFAC-1-700) exhibited the highest specific capacitance of 307 F/g, high salt removal efficiency and electrosorption capacity of 5.74 mg/g when voltage of 2 V was applied. When JFAC electrodes were studied for natural water defluoridation, it was found that JFAC CDI electrodes could remove fluoride (Fˉ) from natural water containing low Fˉ concentrations to the permissible limits set by the World Health Organization (WHO). Maximum Fˉ adsorption efficiency (62%) and electrosorption capacity (0.13 mg/g) were attained with applied voltage of 2 V and the pH of water remained unaffected. These results indicated that the Artocarpus heterophyllus peels can be the promising CDI electrode materials for low salinity water desalination and defluoridation