Adsorptive removal of various phenols from water by South African coal fly ash

South African coal fly ash (SACFA) was used to effectively remove phenol, 2-nitrophenol and 4-nitrophenol from wastewater. The rate of adsorption follows first-order kinetics before attaining equilibrium with the sorption rate (Kad) obtained being the  highest for 4-nitrophenol (p-nitrophenol) (7.0 x 10.3/h), followed by phenol (1.2 x 10.3/h) and 2-nitrophenol (o-nitrophenol) (1.0 x 10.3/h). Batch studies were performed to evaluate the adsorption process, and it was found that the Freundlich isothermeffectively fits the experimental data for the adsorbates better than the Langmuir model, with the fly ash having the highest adsorption capacity of 6.51 X 10-2 mg/g for 4-nitrophenol, 6.00 x 10-2 mg/g for 2-nitrophenol and 6.31 x10-2 mg/g for phenol. The fly ash was found to adsorb 90.2% of phenol, 88.9% of 2-nitrophenol and 92.6% of 4-nitrophenol at an initialconcentration of 20 mg/.. The desorption studies suggested that the desorption of 4-nitrophenol was the most difficult of the three adsorbates to be desorbed. The desorption efficiency was 17.9% for phenol, 18.8% for 2-nitrophenol and 10.2% for 4-nitrophenol. This work proved that SACFA can be used as an efficient adsorbent material for removal of phenol from water and wastewater

A novel application of phosphogypsum: Treatment of a diamond mine\'s slimes tailings

Premier Mine\'s current slimes dam is nearing the end of its operational life. This is aggravated by a large volume of poor quality water in the dam which is not being recycled back into the process. The poor quality water is the result of a stable colloidal suspension formed from the dominant clay species present in the kimberlitic ore body. The main objective of this test work was to clarify the water to improve the quality for reuse. Phosphogypsum has been identified as an alternative coagulant to clarify the slimes dam water at a relatively low cost. Laboratory- and plant-scale test work was done to investigate the optimum gypsum dosage, as well as to determine the most suitable application technique. The test work showed that gypsum can successfully destabilise the colloidal suspension. However, poor settling rates were achieved. This improved when the gypsum was added in a slurry form in two stages. The addition of flocculants to aid in settling did not have the desired effect, with resultant high consumption and operating costs. Toxicity tests indicated no lethality to Daphnia organisms and showed a positive growth in the algae test. The establishment of a monitoring programme will assist in determining the long-term effects of gypsum on the environment. Water SA Vol.32 (4) 2006: pp.489-49

Chloride-binding Effect of Blast Furnace Slag in Cement Pastes Containing Added Chlorides

Corrosion of rebar in concrete is commonly associated with, and to a large degree influenced by, the free chloride concentration in the pore water. It is standard industry practice to add various mineral admixtures such as pulverised fuel ash (PFA), or fly ash, ground granulated blast furnace slag (GGBS) and silica fume (SF), to concrete mixtures to increase the corrosion resistance of the reinforcement in the matrix and its subsequent design life span. Various investigations have reported on the effect of mineral admixtures and additions on chloride binding in cementitious matrices, and the current study contributes further to knowledge in this field. Unlike previous investigations, this study attempted to make a clear distinction between the contributions of the two components in a blended cement consisting of ordinary Portland cement (OPC) and ground blast furnace slag (BFS). These contributions of each component have been quantified. Relationships between the total amount of chloride bound, the level ofBFS additions, and the levels of initial chloride content present in the matrix were determined. It was found that the OPC/BFS blended cement with partial BFS replacements of up to 50% displayed a lower binding capacity than that of the OPC on its own. This observation was derived based on the assumption that the OPC and slag reactions were treated as competing and equivalent and did not take any potential time delays into account, nor the degree of cement hydration. The chloride-binding efficiency by the BFS is dependent on both the BFS partial replacement addition level as well as the initial amount of chloride present in the matrix. It is shown that both the OPC and BFS contribute to chloride binding in cement pastes, depending on the amount of BFS that replace the OPC component in the matrix.Keywords: Chloride binding, granulated blast furnace slag, pore solution, permeability, corrosio

The Corrosion Behaviour of WC-Co-Ru Alloys in Aggressive Chloride Media

Hardmetals possess excellent wear resistance, making them suitable alloys in several industrial applications. Mine waters with both dissolved chloride and sulphate salts can be severely corrosive and can limit the application of hardmetal tools in the mining industry. Ru additions to these alloys can refine and improve selected mechanical properties, but its influence on the corrosion resistance is unknown. A series of WC-Co-Ru alloys was evaluated in different chloride containing media to investigate their corrosion resistance. Standard electrochemical corrosion tests, chronoamperometric measurements, and surface analyses with Raman spectroscopy were conducted. An increasing amount of Ru improves the corrosion resistance of all the alloys. The effect is not as dramatic as that observed with stainless steels containing Ru in corrosive media. In both corrosive media Ru decreased the cathodic Tafel constant and has a retarding influence on the cathodic part of the corrosion reaction. Raman analyses indicated the presence of tungsten oxide, hydrated tungsten oxide compounds, and CoO and Co3O4 formed on the alloy surfaces during the corrosion process

Association of waist circumference with perception of own health in urban African males and females: the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study

Background: Current waist circumference (WC) cut-points of the Joint Statement Consensus (JSC) (male ≥ 94 cm, female ≥ 80 cm) were compared with a recently proposed WC cut-point (RPWC) (male ≥ 90 cm, female ≥ 98 cm). In this study, we aimed to compare the two cut-points to assess the association between central obesity and perception of own health.Method: We determined blood pressure and fasting bloods [glucose, high-density lipoprotein (HDL) and triglycerides] as metabolic syndrome markers for 171 urban teachers. Perception of own health was determined via the General Health Questionnaire-28 (GHQ-28) to indicate probable psychological distress or a psychiatric disorder or caseness (≥ 4).Results: The RPWC was an improved discrimination between the WC groups on perception of own health as reflected in the GHQ-28 subscales. In the male group, higher scores were found in the RPWC high WC group (≥ 90 cm) with regard to somatic symptoms, social dysfunction and GHQ-28 caseness, compared to those of the low WC groups (< 90 cm). Compared to the RPWC high WC females (≥ 98 cm), the low WC (< 98 cm) reflected significantly higher anxiety and sleeplessness subscale scores.Conclusion: Our results suggest that the RPWC (men 90 cm, women 98 cm), (determined in this African cohort when adding GHQ-28 caseness as a discriminatory variable between WC cut-point), distinguished better between WC groups based on their perception of own health than the JSC cut-point

The quantification of di-octyl terephthalate and calcium carbonate in polyvinyl chloride using Fourier transform-infrared and Raman spectroscopy

The polyvinyl chloride (PVC) industry relies heavily on material property testing during the development of a product. Many of these testing procedures are outdated and time-consuming, resulting in high financial input. Non-destructive, fast, easy-to-use testing methods can significantly reduce the time required to quantify raw materials. We explored alternative analysis techniques, Fourier transform-infrared (FT-IR) and micro-Raman spectroscopy to quantify the main components within a plasticised PVC (pPVC) compound with dioctyl terephthalate (DOTP) plasticizer and calcium carbonate filler. This can reduce costs in the testing and development of new products up to 50%. We prepared 36 samples with varying proportions of DOTP and calcium carbonate and analyzed them using a Raman Microscope and FT-IR Spectrometer. We found a strong correlation (R2 = 0.923) between DOTP and FT-IR spectroscopy data, as well as a strong correlation (FT-IR R2 = 0.910; Raman R2 = 0.813) between the calcium carbonate and data obtained with both spectroscopies. We reported for the first-time correlations that could be used to determine the raw material levels within pPVC provided by both techniques. Five samples were then made and tested, showing some success in the quantification. This study provided a solid baseline for reducing the time taken to make a recommendation from >168 h to <1 h and therefore reducing the costs of product development by up to 50%

ZIF-11 derived nanoporous carbons with ultrahigh uptakes for capture and reversible storage of volatile iodine

© 2019 Elsevier Inc. In this work, three nanoporous carbon materials Z11-700, Z11-800 and Z11-900 were synthesized by a one-step calcination of zeolitic imidazolate framework-11 (ZIF-11) at 700, 800 and 900 ​°C, respectively. The samples obtained were characterized by SEM, PXRD, FT-IR, Raman spectra and N2 adsorption. The results showed that the three ZIF-11 derived samples were micro/mesoporous and had high BET surface areas and pore volumes. Of the synthesized samples, Z11-900 displayed an excellent iodine vapour uptake of 3775 ​mg/g which was superior compared with Z11-700 and Z11-800, as well as other reported solid state materials. What is more, the regeneration efficiency of Z11-900 for iodine molecules was near to 90% (3672 ​mg/g) after three cycles of reuse. The easy operation, highly-effective and recyclable features enable the ZIF-11 derived nanoporous carbons to be a promising adsorbent for applications in environmental remediation

The effect of operating conditions on density stratification in a batch jig II: The influence on stratification kinetics

This paper presents the second of a two part study on density stratification in a laboratory batch jig. The first study, reported elsewhere, investigated the effect of operating conditions on the stratification profile achieved at equilibrium. The study reported in this paper investigated their effect on the kinetics of density stratification under 18 different sets of conditions—5 for binary systems with different particle densities; and 13 for a ternary system with different configurations of the jig cycle. Although the study was academic in nature (it involved simple systems of 8 mm glass beads) it has provided insights into stratification dynamics that have significant practical implications. It has shown that reasonable rates of stratification can be expected in systems with density differences as low as about 150 kg/m3 provided sufficient jigging time is allowed. In addition, the study found that the quality of a density separation achievable in a jig is determined primarily by the properties of the feed to the jig and its mechanical configuration and not so much by how the operating variables of the jig are manipulated or ‘fine-tuned’. The extent to which what is achievable is actually achieved is dependent on stratification kinetics which are determined by both particle properties and the operating conditions in a jig

Design, Construction and Performance Reliability Verification Evaluation of a High Pressure Volumetric Sorption System for CO2 Sorption In South African Coals

High pressure sorption equipment are based on the gravimetric or volumetric principle method of gas sorption onto a specific sorbent. This paper discusses the design, construction and performance consistency testing that was conducted on a recently constructed in-house high pressure volumetric sorption system (HPVSS) in South Africa (SA) which was used for the evaluation of supercritical carbon dioxide (CO2) sorption on SA coals. A detailed description of the equipment, the commissioning phase, leak testing evaluation, estimation of sample, reference and void volume, as well as the method of conducting the measurements of the sorption isotherms are explained. Six (6) South African (SA) coals were selected based on their myriad of properties i.e. coal rank, coal type, and petrographic and proximate analyses. The samples were used as the sorbing material for pure CO2 in supercritical phase to conduct the isothermal sorption investigations. In order to evaluate the system, multiple reliability experimental runs were conducted and the isotherms were evaluated and the sorption data was verified using the one-way analysis of variance method (ANOVA) to ensure the equipment performance was statistically reliable. Both the, system temperature and pressures, were varied to determine the potential risks of leaks in order to validate the consistency of the system at varying conditions of supercritical gas injection. For the total number of experimental test runs that were conducted, was observed that very good repeatability of the sorption data was reproduced under all conditions. The data exhibited good homogenous variance in all data sets compared, thus demonstrating overall confidence in the repeatability of these CO2 results, and that the reliability of the HPVSS has been confirmed in the test sorption experiments. A comparison to both national and international published data sets also confirmed good fit of the findings

Electrochemical corrosion behaviour of different grades of wc-co, high-cr white cast irons and hadfield steel in 1 m sulphuric acid

Electrochemical polarisation tests were carried out on three grades of WC-Co cemented carbides to investigate the corrosive behaviour of the hardmetals and rank them as viable protective liners for chutes and skips in the mining industry. The cobalt binder content and WC particle size varied. The binder content ranged from 6–12 wt%, and the grain size of the WC particles ranged from 0.4–2.3 µm. The performance of the WC-Co hardmetal was compared to three different grades of high chromium white cast irons and Hadfield steel. The cast irons varied in both their chromium content and the morphology of the Cr-rich primary carbides. Potentiodynamic polarisation and linear polarization resistance scans were used to determine the corrosion current density and other electrochemical parameters. The microstructural characteristics of the samples were analysed using Scanning Electron Microscope(SEM) with Energy Dispersive Spectroscopy (EDS), and optical microscopy. The potentiodynamic scans revealed that, although the WC-Co alloys were found to have generally improved corrosion resistance, it was the high-Cr white cast iron (22 wt% Cr) that recorded the lowest corrosion current density and therefore displayed the best resistance against corrosive attack in 1 M H2SO4. The Hadfield steel exhibited the poorest resistance to corrosion and therefore, suffered the most degradation to its exposed surface