The overall objective of the activity is to contribute to the development of the quest for simple, low-cost and high-performance water purification processes using diverse materials (clay minerals, laterite soils, oxide materials and Nano-oxide materials). These materials are good adsorbents and inexpensive and represent a viable replacement to the chemicals for the removal of some metalloids and heavy metals cations such as arsenic, mercury and thallium ions from groundwater and surface water in some localities of Burkina Faso. The natural materials are also modified to obtain good adsorbents for the removal of organic pollutants such as endocrine disruptors (EDs) from waste water and groundwater. The relevance of the project is related to the use of knowledge in Science and Technology to ensure access to clean and safe water in rural environments of Burkina Faso as stated in the Millennium Development Goals (MDG’s) (UN Millennium project, 2005). It is then obvious that science and technology could play an important role in ensuring access to safe water. From this point of view, our research activity suits very well with Sida’s strategies to fight against poverty. Our activity also suits with policy and strategies adopted at the national authority for water resources in Burkina Faso to fight against poverty. The specific objectives assigned to the project are as follows: (i) assessing the level of different pollutants (Hg, As(III, V), Tl(I,III), and endocrine disruptors (BPA)) in aqueous matrices (ground water, water bodies, and surface water), sediments and vegetables by using novel electrochemical methods; (ii) Characterizations of materials (clay minerals, laterite soils, modified organoclays, oxide materials, and Nano-oxide materials) and their usage for water purification: arsenic, Hg, thallium ions, and endocrine disruptors removal from aqueous matrices.

In relation to the overall goal of the project, two specific objectives were defined for the period 2021-2023. For each specific objective, we will give a summary of the progress which has been achieved during the period 2021-2023.

Specific objectives 1: water analysis with respect to trace contaminants in order to assess their level in groundwater and wastewater in some localities of Burkina Faso: thallium and endocrine disruptors were determined using electrochemical methods.

 Main achievements and results regarding the specific objectives 1 during the period 2021-2023.

1) Thallium assessment in groundwater
We carried out the functionalization of carbon paste electrodes impregnated with wax and modified by a deposition of mercury. The wax composition as well as the optimal parameters for mercury film deposition and thallium (I) analysis were determined. The content of 5% wax and 37.5% binder (silicone oil) is suitable for a good sensor sensitivity. The thallium deposits were made under the following conditions: deposition potential = -1200mV, deposition time = 360 s, electrode stirring speed = 1000rpm. The RSD (Relative Standard Deviation) for a Tl concentration of 10−6 mol/L and for 5 measurements is 1.3%, the detection limit is estimated at 9, 2.10−9 mol/L and the dosage of a certified standard of thallium at 1 mg / L leads to a recovery rate of 99.55%. The detection limit obtained is 10−6 mol/L. Compared to other sensors reported in the literature, the carbon paste electrode has been shown to be effective for the determination of traces of thallium (I). In addition, the extension of the sensor to other metals such as copper (II), lead (II) and cadmium shows that it is also a potential electrode for the determination of ions of these metals. The sensor was subsequently successfully applied to real water and saprolite samples sampled in the village of Yamtenga.

2) Endocrine disruptors (BPA) determination in waste waters using novel electrochemical methods
The objective of this work was twofold. Firstly, we built and modified electrodes:
• in conventional carbon paste (EPC) with cobalt phthalocyanine/histidine composite (CoPc-His);
• in conventional carbon paste with manganese phthalocyanine/histidine (MnPc-His) composite;
• in hybrid-bonded carbon paste (EPC-LI) with cobalt phthalocyanine (CoPc) and
• Hybrid-bonded carbon paste with graphene oxide nanosheets (GO).

Secondly, the modified electrodes were characterized by cyclic voltametry (CV), electrochemical impedance spectroscopy (EIS), chronocoulometry (CC), scanning electron with microscopy/energy dispersive X-ray spectrometry (SEM/EDX), Fourier transform infrared (FTIR), UV-visible spectroscopy and X-ray diffraction (XRD) to assess their performance and understand the mechanisms of BPA oxidation at the interface.
Under optimized experimental conditions, square-wave voltametry (SWV) was used as a sensitive analytical method for the determination of bisphenol A. Measurements taken on tap water, mineral water in plastic bottles, water in plastic sachets, dam water and wastewater from the plastics industry in the Ouagadougou region indicate the presence of BPA.

Specific objectives 2: local materials investigations (laterite soils, Alumina Nanoparticles) and their use for water purification:

 Main achievements and results regarding the specific objectives 2 during the period 2021-2023.
1) Removal of As(III) using a natural laterite fixed-bed column intercalated with activated carbon

Significance of the research: This work was dedicated to the field of As(III) removal by adsorption using a laterite fixed-bed column intercalated with activated carbon. Indeed, arsenic health problem has occurred in the Northern part of Burkina Faso due to groundwater contamination by this pollutant. Although several conventional techniques exist for arsenic contaminated water treatment, they are very difficult to implement in developing countries because of their high cost, the sophisticated technology which is involved, and the risks of toxicity in some circumstances. In our context, there is an urgent need to find low-cost and efficient processes for the treatment of contaminated water by using natural materials from the country.

Natural laterites have been the subject of a lot of investigations since they were shown to have potential applications in arsenic removal from groundwater. Many papers have documented arsenic removal by adsorption on natural laterite using batch and fixed-bed column experiments. Contrary to previous investigations in the literature, our work showed that the fixed-bed column investigations encountered some issues, in particular the clogging of the column by small lateritic particles which can slow down the water flow through the column in the long run. To the best of our knowledge, this work envisages for the first time the clogging issue in a fixed-bed column, which is only filled with laterites particles. As a result, our work investigated a new low-cost filter system, which is based on laterites layers alternated with activated carbon layers and likely to overcome the clogging problem occurring when As(III) solution is percolating through the fixed-bed column. The activated carbon was prepared from local biomasses such as Balanites aegyptiaca cores. These Balanites aegyptiaca cores, as well as the natural laterites, are widely available in the country and can be easily collected and valorized as raw materials. It is worth noting that it’s the first time that activated carbon, prepared from local biomasses such as Balanites aegyptiaca cores, is used as alternated layers in a process of arsenic contaminated water treatment.

This new low-cost filter system permitted to avoid the column clogging by laterite particles. Our new system has the advantage of being applied for arsenic removal in real waters because of its ability to adapt to multiple processes, which can reduce treatment and operating costs. The operational parameters for the improvement of the As(III) removal capacity were investigated and were found to be: a minimum depth of Zmin value set at 15.23 cm with an intercalation activated carbon height of 25 %, a granulometry of laterite ranging from 0.4 and 0.9 mm and an adsorbent dose of As(III) ranging from 0.5 to 2 mg/L. We correlated the experimental data with theoretical breakthrough curve models to predict the overall adsorption behavior. A comparison of the Bohart-Adams adsorption capacity obtained in this study with those reported for other laterite adsorbents indicated that alternating the activated carbon layers and the natural laterite provided a higher adsorption capacity. The characterization of both intercalated and non-intercalated laterite was carried out by investigating the modification of the hydraulic conductivity as its measurement can be carried out at a low-cost and is easy to implement. The present investigations provided data which appropriately justify the modification of the permeability of the porous system when the laterite bed system is intercalated by activated carbon layers.
The novelty of the present work can be seen from the use of a natural laterite fixed-bed column intercalated with activated carbon, which solves for the first time the clogging problem occurring during the percolation process through a fixed-bed column filled by laterites particles. Moreover, the characterization of the hydraulic property of the natural laterite fixed-bed column intercalated with activated carbon may lead to an appropriate justification when the screening of such a porous filter column for use in pollutant removal is made.

2) Nano alumina materials synthesis and their subsequent use for thallium removal from groundwater

Gamma alumina nanoparticles, synthesized from natural bauxite from Burkina Faso, were used to remove thallium (I) and bisphenol A in synthetic solutions in batch mode. Before the batch mode investigations, the alumina nanoparticles were characterized by different physicochemical methods (DRX, FTIR, elementary chemical analyzes, SEM, AFM etc.). For an initial concentration of 20 µg/L and an adsorbent dose of 1 g/L at a pH value of 8.5, the removal rate of Tl(I) was 95.12 ± 0.02%. It has been shown that alumina nanoparticles adsorb very well traces of thallium (I) with a maximum drawdown rate in a basic medium, and the adsorption capacity decreases for pH values less than 8 or greater than 10. Kinetic and isothermal models were studied. We found that the pseudo-second order model as well as the Freundlich isotherm described better the experimental results. The analysis of the intra-particle diffusion model shows a multi-linearity suggesting that the external mass transfer and the intra-particle diffusion are involved in the different stages of Tl(I) sorption. The process of thallium (I) removal may be linked to an electrostatic interaction between Tl(I) and the negatively charged surface of γ-ANPs, Tl(I) being present as Tl+ ion below pH 10. The thermodynamic study showed that the thallium (I) adsorption process was a spontaneous and exothermic reaction with coexistence of physisorption and chemisorption with a dominance of physisorption.

Finally, this work showed that the modification of the alumina synthesized by using CTAB as surfactant leads to a better adsorption performance of BPA with a high adsorption rate. Kinetic and isothermal models were evaluated. We found that the pseudo-second order model as well as the Langmuir isotherm better described the experimental results. The process of adsorption of BPA can be related to a hydrophobic interaction at pH values ranging from 4 to 9.6, and an electrostatic interaction at a pH value of 10. At pH values above 10, the adsorbent surface being neutralized by hydroxyl ions, the interaction between the adsorbent surface and the BPA ions weakens and this leads to the decrease in adsorption. The thermodynamic study showed that the BPA adsorption process was a spontaneous reaction, exothermic and governed by physisorption (van der Waals forces, hydrogen bonding, hydrophobic interactions, π * -π interactions).

The results have been published in the following papers:
• Ollé Rodrigue Kam, Issaka Garikoé, Corneille Bakouan, Boubié Guel,
Low-Cost Synthesis of Alumina Nanoparticles and Their Usage for Bisphenol-A Removal from Aqueous Solutions, Processes (2021), 9, 1709, pages 1-22. https://doi.org/10.3390/pr9101709.
• Ollé Rodrigue Kam, Corneille Bakouan, Inoussa Zongo, Boubié Guel,
Removal of Thallium from Aqueous Solutions by Adsorption onto Alumina Nanoparticles, Processes (2022), 10(9), 1826, pages 1-22. https://doi.org/10.3390/pr10091826.

Current challenge for the period 2024-2026: The challenge will be to carry out the following measurements: X-ray photo electron spectroscopy (XPS) to study the bonds between Nano alumina and thallium after adsorption; Photoluminescence spectroscopy (PLS) to study the nature of defects in Nano alumina materials; Time-resolved fluorescence to study the spatial arrangement of hydroxyls on the material; X-ray fluorescence to assess chemical composition; Thermogravimetric analysis (TGA) to study the thermal behavior of the sample for decomposition and the characteristics of mass loss during calcination.

Uppsala University (Sweden), ARES