Mary B. Ogundiran

Immobilisation of lead smelting slag within spent aluminate-fly ash based geopolymers.

This study presents the solidification/stabilisation and immobilisation of lead smelting slag (LSS) by its incorporation in coal fly ash - blast furnace slag based geopolymers. It also explores the use of a spent aluminium etching solution (AES) as geopolymer activator instead of the commonly used silicate solutions. The compressive strength of the geopolymers produced with the AES was lower than when applying a K-silicate solution as activator (100MPa versus 80MPa after 28 days). Compressive strength was not affected when up to 10% of the FA was replaced by LSS. NEN 12457-4, TCLP, SPLP and NEN 7375 leaching tests indicated that mobile Pb from LSS was highly immobilised. The diffusion leaching test NEN 7375 revealed exceeding of the Dutch Soil Quality Regulation threshold limits only for Se and Sb. On the condition that the remaining excess leaching can be reduced by further refinement of the mixture recipes, the proposed process will have the potential of producing waste-based construction materials that may be applied under controlled conditions in specific situations.

Mobility and speciation of heavy metals in soils impacted by hazardous waste.

Abstract This study describes the mobility and chemical fractionation of heavy metals (HMs) from a site impacted by auto battery slag that was generated from secondary lead smelting operations. Samples were collected from the waste pile and from the immediate surrounding soil at four depths to assess the migration and potential bioavailability of Pb, Cd, Cr, Ni and Zn. Total levels of the HMs and their fractionation were determined. The results indicate that highest levels of HMs are present in the uppermost layer with significant migration down the depth, thereby posing a threat to groundwater quality. In the fractions, the concentrations of the metals follow this sequence: Pb>Zn>Cd>Cr>Ni. The chemical fractions of Pb, Cd, Cr, Ni and Zn in the samples, expressed as mean concentrations of the sum of the individual chemical fractions, demonstrate that the HMs exist mainly in the non-residual fractions. For instance, the percentage of non-residual fractions of lead in the waste pile and the surrounding soil ranged from 48.9 to 95.6% and 69.4 to 98.3% respectively. The mobility factors of the heavy metals are significantly high indicating high potential mobility and bioavailable forms of these HMs. The high concentrations of the HMs particularly Pb in the non-residual fractions, as observed in this study, shows the impact of anthropogenic activities on enrichment of natural soil with bioavailable HMs. Consequently, there is a need to be cautious in the way waste that is generated from heavy metals projects is added to natural soil.

Potential environmental hazards of non-rechargeable electric torch wastes in Nigeria

This study assessed the material and chemical compositions and methods of disposal of end-of-life non-rechargeable electric torches (EOLNETs). Thirty EOLNETs of ten different models were collected in Lagos, Nigeria. Total heavy metals in plastic and PWB components of the samples were determined using CPSC-CH-1002-08 and EPA 3050B methods. Questionnaires were distributed to 200 unselected respondents to assess the usage and disposal of EOLNETs. The result showed that plastic is the most abundant component of the waste with a mean composition of 70.9%. The levels of Cd, Cr and Ni were low. The range and mean ± SD concentrations of Pb in the plastics was 282 to 1,910 mg/kg (717 ± 522) and in PWB was 6,060 to 66,200 mg/kg (39,200 ± 20,800) respectively. 86.6% of the respondents use the products. 90.7% respondents disposed their spent torches in dumpsites. This study demonstrates that EOLNETs constitute hazardous e-wastes that require well informed management protocols and effective disposal strategies.

Investigating the Suitability of Nigerian Calcined Kaolins as Raw Materials for Geopolymer Binders

Clay minerals constitute large deposits of natural resources in Nigeria which may exhibit the pozzolanic properties of geopolymer materials. Therefore, this study investigated the suitability of Ikare and Ikere kaolins from two different geological locations in Nigeria as raw materials to synthesis geopolymer binders. In order to ascertain optimal geopolymerization conditions, the effects of calcining temperature, activator concentration and particle size on the compressive strength (engineering) and water absorption (durability) properties of the geopolymers produced were measured at 7 and 28 days at room temperature. The two kaolins with particle sizes 600, 425, 212 µm were calcined at 600°, 700° and 750°C and activated with sodium silicate at SiO2/Na2O mole ratios 2.1, 2.5 and 2.8. The best compressive strength and water absorption were obtained at 700°C calcination temperature, SiO2/Na2O mole ratio 2.1, 212 µm clay particle size and at 28 days curing time. The obtained CS for Ikare and Ikere kaolins at the optimal conditions were 23.2 and 26.1 MPa while water absorption values were 1.62 and 0.12% respectively. Calcined Nigerian kaolins are proposed as cost-effective and sustainable binders which may be applied to substitute or augment ordinary Portland cement in construction applications.

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.