Kaolin Clay-Based Geopolymer for Ionic Thermoelectric Energy Harvesting.

Geopolymers, a class of sustainable inorganic materials derived from natural and recycled resources, hold promise for various applications, including thermoelectric power generation. This study delves into the thermoelectric properties of Ikere white (IKW)-geopolymer, derived from kaolin clay, by employing rigorous measurements of thermal conductivity, electrical conductivity, and Seebeck coefficient. The investigation elucidates the pivotal role of temperature and ions in shaping the thermoelectric performance of IKW-geopolymer. Electrical conductivity analysis pinpoints ions within the geopolymer's channels as primary contributors. Beyond a critical temperature, the evaporation of bulk water triggers a transition of charge carriers from one- to three-dimensional motion, resulting in reduced conductivity. The Seebeck coefficient exhibits a range from -182 to 42 µV/K, with its time-dependent profile suggesting that ions potentially drive thermoelectricity in cementitious materials. Notably, a unique transition from n-type to p-type behavior was observed in the geopolymer, opening new avenues for ionic thermoelectric capacitors. These insights advance our understanding of thermoelectric behavior in geopolymers and have the potential to propel the development of novel building materials for energy conversion applications.

Cool Concrete Incorporating Carbonated Periwinkle Shell: A Sustainable Solution for Mitigating Urban Heat Island Effects.

The urban heat island effect has become a critical issue in urban areas, intensifying heat-related problems and increasing energy consumption. A sustainable cement formulation that combines ordinary Portland cement (OPC) with a carbonated aggregate derived from Periwinkle shell powder for the development of an efficient cool material is presented. Through a carbonation process, the aggregate undergoes a transformation, capturing carbon dioxide (CO2) and converting it into calcite. The resulting cement mixture exhibits high solar reflective properties, making it a potential candidate for cool pavement and roof applications. In this study, the raw materials, including the Periwinkle shell powder, were characterized, and the carbonation process was evaluated to quantify the CO2 capture efficiency. Additionally, a real test of the efficiency of this new cement on a roof demonstrated that the material achieved a significant cooling effect, being 6 °C cooler than that with standard OPC at the peak of solar radiation.

Material and Substance Flow Analysis of Used Lead Acid Batteries in Nigeria: Implications for Recovery and Environmental Quality.

BACKGROUND: As resources become scarce, information from material and substance flow analysis can help to improve material recovery policy. The flow of toxic substances such as lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As) and antimony (Sb) can be used as a basis for appropriate risk management decisions for optimum environmental quality. OBJECTIVES: The present study examined a material and substance flow analysis of used lead acid batteries (ULAB) from motor vehicles and implications for environmental quality in Nigeria. METHODS: Information on motor vehicle imports was obtained from the literature. Mathematical models were constructed and used for the material and substance flow analysis. Samples of 50 brands of ULAB pastes were digested using a microwave digestion system followed by elemental determination (Pb, Cd, silver (Ag), As, cobalt (Co), calcium (Ca), Cr, copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), Sb, selenium (Se), and tellurium (Te)) with inductively coupled plasma optical emission spectroscopy. RESULTS: Approximately 4.8 million tons (Mt) lead acid batteries (LAB) from vehicles was used in Nigeria between 1980 and 2014, out of which approximately 2.6 Mt had reached end-of-life (EoL) stages. From the total amount in EoL, approximately 2.3 Mt was recycled, and 0.3 Mt was landfilled. Among the toxic elements, Pb, Cd and As were the most abundant in ULAB; and of the valuable elements, Fe and Cu had the highest levels. Approximately 3.5 Mt of Pb was used in the past (1980-2014) in ULAB for motor vehicles, out of which approximately 1.9 Mt tons was in EoL stages. DISCUSSION: The results revealed that the battery pastes were heterogeneous. Only Pb exceeded the total threshold limit concentration (TTLC) of 1000 mg/kg. The TTLC describes the safe levels or concentration of heavy metals in the environment. The levels observed for other metals in this study were below the TTLC values. The present study estimated an average life span for lead acid batteries in motor vehicles in Nigeria of 5 years, suggesting an additional 2.2 Mt at EoL by 2019. High concentrations of Pb in air, water and soil carry the potential for contamination of food products, especially in Nigeria, where food is traditionally prepared and sold in open air markets in an unregulated manner. CONCLUSIONS: High amounts of toxic elements present in the various life cycle stages signal potential environmental and human health hazards. COMPETING INTERESTS: The authors declare no competing financial interests.

Assessment of Ordinary Kriging and Inverse Distance Weighting Methods for Modeling Chromium and Cadmium Soil Pollution in E-Waste Sites in Douala, Cameroon.

BACKGROUND: Several studies have demonstrated that chromium (Cr) and cadmium (Cd) have adverse impacts on the environment and human health. These elements are present in electronic waste (e-waste) recycling sites. Several interpolation methods have been used to evaluate geographical impacts on humans and the environment. OBJECTIVES: The aim of the present paper is to compare the accuracy of inverse distance weighting (IDW) and ordinary kriging (OK) in topsoil analysis of e-waste recycling sites in Douala, Cameroon. METHODS: Selecting the proper spatial interpolation method is crucial for carrying out surface analysis. Ordinary kriging and IDW are interpolation methods used for spatial analysis and surface mapping. Two sets of samples were used and compared. The performances of interpolation methods were evaluated and compared using cross-validation. RESULTS: The results showed that the OK method performed better than IDW prediction for the spatial distribution of Cr, but the two interpolation methods had the same result for Cd (in the first set of samples). Results from Kolmogorov-Smirnov and Shapiro-Wilk tests showed that the data were normally distributed in the study area. The p value (0.302 and 0.773) was greater than 0.05 for Cr and for Cd (0.267 and 0.712). In the second set of samples, the OK method results (for Cd and Cr) were greatly diminished and the concentrations dropped, looking more like an average on the maps. However, the IDW interpolation gave a better representation of the concentration of Cd and Cr on the maps of the study area. For the second set of samples, OK and IDW for Cd and Cr had more similar results, especially in terms of root mean square error (RMSE). CONCLUSIONS: Many parameters were better identified from the RMSE statistic obtained from cross-validation after exhaustive testing. Inverse distance weighting appeared more adequate in limited urban areas. COMPETING INTERESTS: The authors declare no competing financial interests.

Ecological Risk and Human Health Implications of Heavy Metals Contamination of Surface Soil in E-Waste Recycling Sites in Douala, Cameroun.

BACKGROUND: Recycling of electronic waste (e-waste) in developing nations poses a risk to the environment and human health through the release of heavy metals. OBJECTIVES: The aim of the present study was to evaluate the levels of heavy metals in Douala, Cameroun, the site of e-waste recycling activities. METHODS: Soil samples were collected from Makea, Ngodi and New Bell e-waste recycling sites, as well as from a control site. Samples were digested and levels of heavy metals were determined. RESULTS: The concentrations of the heavy metals in Makea occurred in the order of lead (Pb) (290±40) > zinc (Zn) (160±30) > chromium (Cr) (130±40) > copper (Cu) (130±20) > nickel (Ni) (56±5.7) > cadmium (Cd) (20±3.0); Pb (310±30) >Zn (150±20) >Cu (80±30) >Cr (70±40) >Ni (50±1.0) >Cd (30±5.0) in Ngodi; and Pb (280±40) >Zn (155±35) >Cu (80±50) >Cr (70±40) >Ni (53±2.0) >Cd (20±10) in New Bell. The levels of metals in all of the samples were higher compared to the control site, which was composed of vegetation and far from the e-waste sites, and in some cases, higher than permissible limits or guidelines. The ecological risk index of heavy metals for soil samples in all the e-waste sites indicated a very high risk. CONCLUSIONS: Heavy metals concentrations in soil around e-waste recycling sites present serious health risks and further investigations are needed. COMPETING INTERESTS: The authors declare no competing financial interests.

Initial Inventory of Plastics Imports in Nigeria as a Basis for More Sustainable Management Policies.

BACKGROUND: Plastic is a waste stream with recycling and recovery potential. However, the recycling rates for plastic in African countries are low. Furthermore, use and production of virgin plastics are increasing. Therefore, a high proportion of plastic waste is being disposed of in landfills and dumpsites. Plastic serves as fuel for open burning at landfills/dumpsites with associated releases and constitutes a large fraction of marine litter, making it a major and growing global pollution concern. OBJECTIVES: This study aims to develop an initial inventory of plastics in Nigeria towards the development of an effective plastics management frame. METHODS: A search was conducted of the recent literature and the United Nations (UN) Comtrade database using harmonized system (HS) codes for import data of various polymer categories and major product categories containing plastic. Algebraic expressions were developed for calculation of the share of plastic in these products. RESULTS: Approximately 14,200,000 tons of plastics in primary form were imported into Nigeria between 1996-2014. Approximately 3,420,000 tons total plastic were imported in the form of products and approximately 5,545,700 tons were imported as product components. Approximately 194,000 tons of plastic toys were imported over a six-year period. DISCUSSION: The total amount of plastics imported in primary form and as products equals 17,620,000 tons. The total volume of imported plastic, newly produced plastic and plastic components going into the technosphere was 23,400,000 tons. The huge amount of plastic and other polymers entering the technosphere in Nigeria has important implications for marine litter, pollution, waste management and resource recovery. CONCLUSIONS: A huge volume of plastics has entered the Nigerian technosphere, with less than 12% of the resulting waste entering the recycling stream. There is a need for sustainable management of this crucial waste and resource category. Potential mitigating strategies include waste plastic reuse, recycling, waste conversion to energy, and appropriate plastic control policy frameworks. COMPETING INTERESTS: The authors declare no competing financial interests.