Investigation of the suitability of activated and non-activated bentonites from the Imerys Mine (South Africa) for geosynthetic clay liners

Geosynthetic clay liners (GCLs) have become a suitable substitute for compacted clay liners used for prevention of leachate percolation from landfills and tailings dams into the groundwater system. The characteristics of most bentonites is improved through a process of activation by mixing with soda ash (Na2CO3). This paper presents the investigation results of the suitability of bentonites from the Imerys Mine in South Africa for use in GCLs. Both activated and non-activated bentonites were investigated through X-ray diffraction (XRD) analysis and swell index, fluid loss, plate water absorption and Atterberg limits tests. The XRD analysis results indicate that the activated and non-activated bentonite have a smectite content of 58% and 67%, respectively. The swell index of non-activated bentonite was significantly lower than that of activated bentonite. The activated bentonite samples tested at different times subsequent to activation revealed that a minimum of 4 weeks of activation time is required to fully activate it to the ideal soda ash to bentonite ratio of 1:16. The fluid loss tests displayed results slightly above the required minimum of 18 mL because of the low swell index of the bentonites tested. The activated and non-activated bentonites have absorption capacities of 133% and 121%, respectively. The plasticity index of the activated bentonite is 101%, 15% higher than the non-activated bentonite. The overall results concluded that the Imerys bentonite is a medium-quality bentonite with borderline index properties that requires at least 4 weeks of beneficiation to achieve complete activation to suitably be used as GCLs. Significance: The significance of this paper is the beneficiation process of bentonite in the geotextile industry. This study is relevant to geotechnical engineers, environmental geologists, engineering geologists and other related professionals working with geosynthetic clay liners whereby bentonite is the key ingredient. The study provides an optimum ratio of bentonite to sodium carbonate and the required time for beneficiation. We further recommend that quality control measures should be implemented to ensure complete activation of bentonite, including the blending process of different qualities of bentonite

Determinants of recovery time from severe acute malnutrition among cholera-exposed and unexposed children in Ethiopia: a prospective cohort study

BackgroundThere is a vicious interplay between severe acute malnutrition (SAM) and diarrheal diseases including cholera. The lack of sufficient evidence on the time to recovery and its determinants among children with cholera prompted this investigation. The study aimed to evaluate the time to recovery and determinants among children with severe acute malnutrition, comparing cholera-exposed and unexposed children.MethodsA prospective cohort study was carried out from September 10, 2022, to February 21, 2023, among 224 children below 15 years. The study was conducted at cholera treatment centers and nearby communities in the Bale and Guji Zones of Oromia Regional state in Ethiopia. A structured questionnaire was used to obtain information and anthropometric measurements were conducted weekly. After checking all assumptions, a multivariable Cox Proportional Hazards model was used to identify independent determinants of time to recovery using an adjusted hazard ratio (AHR) with a 95% confidence interval (CI). Statistical significance was declared at p < 0.05.ResultsNearly 80% of participants recovered from SAM with a recovery rate of 40/1000 person-week observation and a median time to recovery of 21 days [Inter Quartile Range14-28]. The recovery time from SAM for cholera-exposed children was delayed by 54% [ARR: 0.46, 95% CI: 0.30–0.69] compared to unexposed children. Similarly, the recovery time from SAM for food-insecured families was delayed by 39% [ARR: 0.61, 95% CI: 0.38–0.96] compared to food-secured families. Moreover, children with more than three meal frequencies per day had 1.61 times [ARR: 1.61, 95% CI: 1.04–2.50] higher probability of fast recovery from SAM, compared to children with less than three meals. Children from families with good attitudes toward nutrition had more than two times [ARR: 2.23, 95% CI: 1.45–3.41] higher probability of faster recovery from SAM than families with poor attitudes.ConclusionThe study revealed that cholera exposure is one of the main determinants of prolonged recovery time for children with SAM. Food insecurity, meal frequency, and the attitude of parents toward children’s dietary habits were determinants for the recovery of children from SAM. The findings imply the need for designing interventions to enhance child feeding during cholera illness, focusing on key determinants

Assessment of Meteorological Drought and Wet Conditions Using Two Drought Indices Across KwaZulu-Natal Province, South Africa

South Africa has been experiencing a series of droughts for the last few years, limiting the availability of water supply in reservoirs and impacting many sectors of the economy. These droughts have affected even the wetter eastern provinces including KwaZulu-Natal. This paper presents the results of analyses and assessment of meteorological drought across KwaZulu-Natal (KZN) Province of South Africa using two drought indices. The main objective of the study is to understand the changes in rainfall patterns for a period of 48 years (i.e., 1970 to 2017) and identify wet and dry years. The percent of normal precipitation index (PNPI) and rainfall anomaly index (RAI) were used to explore and categorize the wet and dry periods at 18 selected rainfall gauging stations across the province. Mann–Kendall statistics and Sen’s slope were employed on the indices to further understand the trend of drought conditions. The results revealed that 1992 and 2014/15 were the most extremely dry years with 2015 being the driest year over the studied period induced by El Niño. The extremely wet periods were 1987, 1996, and 2000 which have been associated with cyclonic events. Droughts have become more frequent and intense, while wet conditions are less frequent. The drought condition was observed not to be peculiar to one region and to vary from year-to-year. These variations have been associated with global climate drivers including El Niño-southern oscillation (ENSO) and sea surface temperature (SST) conditions. The northern region around Magudu, Hlobane, Vryheid and Dundee were relatively the most affected during periods of extreme drought conditions. Comparative analysis showed that RAI is more robust than PNPI in understanding drought conditions. Thus, it can be applied effectively in Southern Africa in analyzing dry and wet conditions.</jats:p

Investigation of the suitability of activated and non-activated bentonites from the Imerys Mine (South Africa) for geosynthetic clay liners

Geosynthetic clay liners (GCLs) have become a suitable substitute for compacted clay liners used for prevention of leachate percolation from landfills and tailings dams into the groundwater system. The characteristics of most bentonites is improved through a process of activation by mixing with soda ash (Na2CO3). This paper presents the investigation results of the suitability of bentonites from the Imerys Mine in South Africa for use in GCLs. Both activated and non-activated bentonites were investigated through X-ray diffraction (XRD) analysis and swell index, fluid loss, plate water absorption and Atterberg limits tests. The XRD analysis results indicate that the activated and non-activated bentonite have a smectite content of 58% and 67%, respectively. The swell index of non-activated bentonite was significantly lower than that of activated bentonite. The activated bentonite samples tested at different times subsequent to activation revealed that a minimum of 4 weeks of activation time is required to fully activate it to the ideal soda ash to bentonite ratio of 1:16. The fluid loss tests displayed results slightly above the required minimum of 18 mL because of the low swell index of the bentonites tested. The activated and non-activated bentonites have absorption capacities of 133% and 121%, respectively. The plasticity index of the activated bentonite is 101%, 15% higher than the non-activated bentonite. The overall results concluded that the Imerys bentonite is a medium-quality bentonite with borderline index properties that requires at least 4 weeks of beneficiation to achieve complete activation to suitably be used as GCLs. Significance: The significance of this paper is the beneficiation process of bentonite in the geotextile industry. This study is relevant to geotechnical engineers, environmental geologists, engineering geologists and other related professionals working with geosynthetic clay liners whereby bentonite is the key ingredient. The study provides an optimum ratio of bentonite to sodium carbonate and the required time for beneficiation. We further recommend that quality control measures should be implemented to ensure complete activation of bentonite, including the blending process of different qualities of bentonite

An Overview of Aquifer Physiognomies and the δ18O and δ2H Distribution in the South African Groundwaters

A comprehensive assessment of the stable isotope distribution in the groundwater systems of South Africa was conducted in relation to the diversity in the aquifer lithology and corresponding hydraulic characteristics. The stable isotopes of oxygen (18O) and hydrogen (2H) in groundwater show distinct spatial variation owing to the recharge source and possibly mixing effect in the aquifers with the existing water, where aquifers are characterized by diverse hydraulic conductivity and transmissivity values. When the shallow aquifer that receives direct recharge from rainfall shows a similar isotopic signature, it implies less mixing effect, while in the case of deep groundwater interaction between recharging water and the resident water intensifies, which could change the isotope signature. As aquifer depth increases the effect of mixing tends to be minimal. In most cases, the isotopic composition of recharging water shows depletion in the interior areas and western arid zones which is attributed to the depleted isotopic composition of the moisture source. The variations in the stable isotope composition of groundwater in the region are primarily controlled by the isotope composition of the rainfall, which shows variable isotope composition as it was observed from the local meteoric water lines, in addition to the evaporation, recharge and mixing effects.</jats:p