RESUMEN
Over the years, spent potlining (SPL) treatment has only focused on the extraction of its hazardous compounds, especially fluorides and cyanides. The literature has not sufficiently addressed the optimization and kinetics of fluoride extraction using statistical modeling to determine relevant factors for efficient, cost-effective, and sustainable SPL treatment. Hence, this study is focused on response surface methodology (RSM) combined with central composite design (CCD) to statistically model fluoride extraction of SPL behaviour in acidic environments. Shrinkage core model (SCM) was used to investigate the kinetics of fluoride extraction. The RSM analyses suggested a second-order quadratic model with outstanding accuracy, statistically supported by R2 and adjusted R2 values of 0.986 and 0.973, respectively. The quadratic model indicates the main factors influencing fluoride extraction, showing the complex interactions of temperature, particle size, acid concentration, and leaching time. These main factors were observed to have significant effects on fluoride extraction, except for particle sizes of the SPL. The optimization process, a key success of this study, achieved fluoride extraction of 87.49% at specific factor levels of 48.43 °C, 0.752 mm, 1.2 M, and 10 min. Subsequently, the SCM investigations suggested that diffusion through a liquid film mechanism best approximates the fluoride extraction kinetic behaviour with R2 > 0.80 across varying temperatures. Investigations into temperature dependence with the Arrhenius plot further validated that the reaction kinetics were principally controlled by diffusion through liquid film, with an activation energy of 36.26 kJ/mol. Integrating these kinetic frameworks provides a novel approach to analyzing and optimizing SPL fluoride extraction. Overall, adopting the present study in the industrial settings with the optimized parameters will ensure efficient, sustainable, and cost-effective treatment of SPL.
Asunto(s)
Fluoruros , Fluoruros/química , CinéticaRESUMEN
Remedial action for heavy metal-contaminated soils is imperative for preventing heavy metal leachability and minimizing environmental risks. This study evaluated the use of limekiln dust (LKD) as a heavy metal stabilization agent for Ghanaian gold mine oxide ore tailing material. Heavy metal-laden tailing material (Fe, Ni, Cu, Cd, and Hg) was collected from a tailing dam site in Ghana. Stabilization was done using acid neutralization capacity (ANC) and citric acid test (CAT) while all chemical characterization was done using X-ray fluorescence (XRF) spectroscopy. Various physicochemical parameters including pH, EC, and temperature were also measured. The contaminated soils were amended with LKD in doses of 5, 10, 15, and 20 wt.%. The results revealed that the contaminated soils had concentrations of heavy metals above FAO/WHO stipulated limits of 350, 35, 36, 0.8, and 0.3 mg/kg for Fe, Ni, Cu, Cd, and Hg, respectively. After 28 days of curing, 20 wt.% of LKD was found to be appropriate for the remediation of the mine tailings of all the heavy metals studied except Cd. Ten percent of the LKD was noticed to be enough in remedying soil contaminated with Cd since the Cd's concentration reduced from 9.1 to 0.0 mg/kg with a stabilizing efficiency of 100% and a leaching factor of 0.0. Therefore, remediation of contaminated soils of Fe, Cu, Ni, Cd, and Hg with LKD is safe and environmentally friendly.
Asunto(s)
Mercurio , Metales Pesados , Oro , Ghana , Cadmio , Monitoreo del Ambiente , Polvo , Óxidos , SueloRESUMEN
Improper discharge of cassava mill effluent (CME) has attracted much attention in major cassava-producing areas due to cyanide contamination. This study conducted a target survey on inhabitants and processors of the Akrofrom-Techiman cassava processing area in Ghana that aimed to assess their knowledge and perception of cyanide contamination from the CME discharge. The study further examined the effect of CME on the soil and groundwater at the processing area using physicochemical and bacteriological characterizations. Results revealed that inhabitants and processors exhibited high illiteracy on the impact of CME on cyanide contamination in the processing area. The study also indicated a wide characteristics of the soil at the processing site: pH (4.89-8.77), electrical conductivity (EC) (1063.00-1939.00 µS/cm), total dissolved solids (TDS) (523.90-963.50 mg/L), soil moisture (11.90-31.70%), free cyanide (0.02-0.33 mg/kg), and total cyanide (0.40-2.70 mg/kg). Results also showed that the physicochemical values of the CME were all above the Ghana Environmental Protection Agency (EPA) permissible limits and were unsafe for discharging into the environment. The range of physicochemical and bacteriological parameters of the two boreholes revealed the following: pH (7.85-8.74), TDS (165.77-192.37 mg/L), EC (320.87-396.20 µS/cm), free cyanide (0.13-0.16 mg/L), total cyanide (1.29-2.15 mg/L), and bacteriological parameter (220-622 cfu/mL). The two hand-dug wells also recorded pH (8.54-9.56), TDS (140.77-156.10 mg/L), EC (288.53-340.67), biological oxygen demand (BOD) (21.51-1.61 mg/L), chemical oxygen demand (COD) (13.5-16.5 mg/L), free cyanide (0.10-0.11 mg/L), bacteriological parameter (241-302 cfu/mL), and total cyanide (0.79-0.86 mg/L). The study concluded that the discharge of CME at the processing site contributes significantly to cyanide contamination of the soil and groundwater at the processing area.
Asunto(s)
Agua Subterránea , Manihot , Contaminantes Químicos del Agua , Cianuros , Monitoreo del Ambiente , Ghana , Contaminantes Químicos del Agua/análisis , SueloRESUMEN
Trace metals contamination has recently been a major issue due to its damaging effects on public health and environmental receptors. This study focussed on the health risk assessment of trace metals (As, Pb, Cr, and Ni) associated with the direct intake of some selected food crops (namely cocoyam and plantain) at Abuakwa South Municipal, Ghana. The food crops and soil samples were selected randomly from three reclaimed mined sites and one non-mining site in the study area. Results from the trace metal concentration analyses in the soil samples showed that As, Cr, and Ni were above the control. The daily intake of metals (DIM), target hazard quotient (THQ), and carcinogenic risk (CR) assessments of health risks accompanied by the continuous ingestion of the selected food crops polluted through these trace metals were evaluated. 0.23 mg/kg and 0.05 mg/kg, 0.11 mg/kg and 0.02 mg/kg, 0.78 mg/kg and 0.65 mg/kg, and 0.23 mg/kg and 0.09 mg/kg were recorded for As, Cr, Ni, and Pb in that order in the cocoyam and plantain, respectively. The As and Pb concentrations in the food crops were above the WHO recommended limits. This implies that individuals within the vicinity are exposed to high levels of As and Pb through food intake which could result in varying health implications. The DIM and THQ for the studied trace metals were below their permissible limits suggesting that there is a tolerable non-carcinogenic adverse health risk level for adults and children within the studied area. In addition, the lifetime probability of contracting cancer by ingesting Ni, Pb, and Cr in plantain grown in the study area is high. It is recommended that regular monitoring of these trace metals in food crops be carried out in preventing their excessive accumulation.