Daubenya alba (Hyacinthaceae, tribe Massonieae), a new species from the Roggeveld, Northern Cape Province

Daubenya alba A.M. van der Merwe, from the edge of the Roggeveld escarpment in the Northern Cape Province, is described as a new species. It resembles D. capensis (Schltr.) A.M. van der Merwe & J.C. Manning in leaf shape, floral structure and the presence of a staminal tube, but is distinguished by its delicate white to pale lilac flowers and lack of a staminal disc

Thermochemical purification of talc with ammonium sulphate as chemical additive

This study reports on the thermochemical reactivity of talc with ammonium sulphate, a low-cost, recyclable chemical additive commonly used in the thermochemical extraction of strategic metals from low-grade ores and industrial and mine residues. The talc sample used in this study contained 70% talc, 15% lizardite and 10% kaolinite, following the removal of carbonate minerals by HCl leaching as a pre-concentration step. The solid product obtained by thermochemical treatment followed by aqueous leaching contained high-grade purified talc (>98%) as the principal mineral phase. It was depleted of lizardite and kaolinite, which had reacted with ammonium sulphate to form water-soluble hydrated ammonium metal sulphates. A comparative analysis of the TGA profiles of the concentrated parent sample, the solid product and the solid residue highlighted an identical mass loss between 850 °C and 1000 °C, which is the temperature range at which the dehydroxylation of talc occurs. This indicated minimal, if any, structural denaturation of the talc phase following thermochemical treatment with ammonium sulphate under the experimental condition studied. This process may therefore represent a promising technology for the purification of talc under the right market conditions, provided the mineral co-exists with phases featuring a high degree of reactivity with ammonium sulphate under thermal conditions.The University of Pretoria and the National Research Foundation of South Africa.http://www.elsevier.com/locate/mineng2022-02-19hj2021Chemistr

Injection of coal fly ash slurry in deep saline formations for improved CO2 confinement : a theoretical concept

98% of South Africa‟s total CO2 geological storage capacity is in the form of deep saline formations located off-shore, while the remaining 2% is situated on-shore. Such formations may not have a similar proven sealing capacity to that of depleted gas and oil reservoirs, and the country must give due consideration to every theoretically conceivable option for CO2 storage. This paper discusses a theoretical concept whereby coal fly ash slurries, composed of homogeneously-sized ultra-fine particles with adequate shear-thinning Newtonian rheological properties when suspended in water, could be injected in deep saline formations, alongside CO2, to engineer a „mineral curtain‟ that could act as a barrier preventing unwanted CO2 migration outside the boundary layers of the reservoir. The resulting pressure build-up could be managed by extracting the brine from the formations, which could then be used to produce fresh water for local communities deprived of drinking water.South African Centre for Carbon Capture and Storage and the Mining Qualifications Authority of South Africahttp://www.elsevier.com/locate/ijggchb201

Thermochemical processing of a South African ultrafine coal fly ash using ammonium sulphate as extracting agent for aluminium extraction

South African coal fly ash represents an untapped secondary resource of aluminium. Continuous research is conducted to develop suitable chemical and/or geometallurgical processes for aluminium extraction, preferably accompanied by minimal silicon extraction. The thermochemical treatment of a South African ultrafine coal fly ash was investigated to test the feasibility of recovering aluminium using ammonium sulphate, a widely available, low-cost, recyclable chemical agent. The optimum processing conditions were determined to be a temperature of 500 °C and a fly ash to ammonium sulphate weight ratio of 2:6 when a reaction time of 1 h was used. Water leaching of the reaction product obtained under these conditions resulted in the selective recovery of 95.0% aluminium from the amorphous phase, with b0.6% Si extracted. Mullite was unlikely to have reacted with the extracting agent. Except for Si, the process was not element-selective, but the extraction of iron could be minimized by increasing the treatment temperature to 600 °C without compromising Al extraction. Thermochemical treatment using ammonium sulphate may therefore represent a promising technology for extracting aluminium from coal fly ash, which could be subsequently converted to value-added products such as alumina.The Council for Geoscience, the University of Pretoria and the National Research Foundation of South Africa (NRF; Grant No. 93641).http://www.elsevier.com/locate/hydromet2017-12-31hb2016Chemistr

The sensitivity of direct faecal examination, direct faecal flotation, modified centrifugal faecal flotation and centrifugal sedimentation/flotation in the diagnosis of canine spirocercosis

Several faecal examination techniques have shown variable sensitivity in demonstrating Spirocerca lupi (S. lupi) eggs. The objective of this study was to determine which faecal examination technique, including a novel modified centrifugal flotation technique, was most sensitive to diagnose spirocercosis. Ten coproscopic examinations were performed on faeces collected from 33 dogs confirmed endoscopically to have spirocercosis. The tests included a direct faecal examination, a faecal sedimentation/flotation test, 4 direct faecal flotations and 4 modified faecal centrifugal flotations. These latter 2 flotation tests utilised 4 different faecal flotation solutions:NaNO3 (SG 1.22),MgSO4 (SG 1.29),ZnSO4 (SG 1.30) and sugar (SG 1.27). The sensitivity of the tests ranged between 42 %and 67 %, with theNaNO3 solution showing the highest sensitivity in both the direct and modified-centrifugal flotations. The modified NaNO3 centrifugal method ranked 1st with the highest mean egg count (45.24±83), and was superior (i.e. higher egg count) and significantly different (P<0.05) compared with the routine saturated sugar,ZnSO4 andMgSO4 flotation methods. The routine NaNO3 flotation method was also superior and significantly different (P < 0.05) compared with the routine ZnSO4 andMgSO4 flotation methods. Fifteen per cent (n=5) of dogs had neoplastic oesophageal nodules and a further 18 % (n = 6) had both neoplastic and non-neoplastic nodules. S. lupi eggs were demonstrated in 40%of dogs with neoplastic nodules only and 72.9 % of the dogs with non-neoplastic nodules. The mean egg count in the non-neoplastic group (61) was statistically greater (P = 0.02) than that of the neoplastic group (1). The results show that faecal examination using a NaNO3 solution is the most sensitive in the diagnosis of spirocercosis. The modified centrifugal flotation faecal method using this solution has the highest egg count. The study also found that dogs with neoplastic nodules shed significantly fewer eggs than dogs with non-neoplastic nodules.The authors would like to thank the Onderstepoort Veterinary Academic Hospital and Faculty of Veterinary Science, University of Pretoria, for their support and financial assistance towards this project, and the South African Veterinary Foundation (SAVF) for financial assistance to the S. lupi project at Onderstepoort.http://www.journals.co.za/ej/ejour_savet.htm

Preparation of sodium silicate solutions and silica nanoparticles from South African coal fly ash

Please read abstract in the article.UNISA, University of Pretoria, Council for Geoscience, and the National Research Foundation of South Africa (NRF; Grant No.93641).https://link.springer.com/journal/126492020-06-20hj2020Chemistr

A Partial-Closure Canonicity Test to Increase the Efficiency of CbO-Type Algorithms

Computing formal concepts is a fundamental part of Formal Concept Analysis and the design of increasingly efficient algorithms to carry out this task is a continuing strand of FCA research. Most approaches suffer from the repeated computation of the same formal concepts and, initially, algorithms concentrated on efficient searches through already computed results to detect these repeats, until the so-called canonicity test was introduced. The canonicity test meant that it was sufficient to examine the attributes of a computed concept to determine its newness: searching through previously computed concepts was no longer necessary. The employment of this test in Close-by-One type algorithms has proved to be highly effective. The typical CbO approach is to compute a concept and then test its canonicity. This paper describes a more efficient approach, whereby a concept need only be partially computed in order to carry out the test. Only if it passes the test does the computation of the concept need to be completed. This paper presents this ‘partial-closure’ canonicity test in the In-Close algorithm and compares it to a traditional CbO algorithm to demonstrate the increase in efficiency

Characterisation of the hydration products of a chemically and mechanically activated high coal fly ash hybrid cement

Cement companies are significant contributors of the planet’s anthropogenic CO2 emissions. With increased awareness of the substantial volume of CO2 emissions from cement production, a variety of mitigation strategies are being considered and pursued globally. Hybrid cements are deemed to be technologically viable materials for contemporary construction. They require less clinker than that for ordinary Portland cement, leading to a decrease in CO2 emissions per tonne of hybrid cement manufactured. The hybrids produced in this study consist of 70% siliceous coal fly ash and 30% Portland cement, and combines chemical (sodium sulphate) and mechanical (milling) activation. The aim of this work was to develop a better understanding of the hydration products formed and the resulting effect of activation on these hydration products, of hybrid coal fly ash cement pastes over an extended curing period of up to one year. The results indicated that chemical activation increases the formation of stable, well crystallised ettringite. Chemical activation as well as mechanical activation increased the rate of the pozzolanic reaction between portlandite contained in cement and coal fly ash. The application of combined chemical and mechanical activation definitely resulted in the fastest rate of portlandite consumption, hence an increased rate of the pozzolanic reaction.The National Research Foundation of South Africa.https://www.mdpi.com/journal/mineralsam2023ChemistryCivil Engineerin

Influence of hydrating agents on MgO hydration

BACKGROUND: The influence of different hydrating agents on the pH of the hydrating solutions, rate of hydration of MgO to Mg(OH)2 and product surface area was studied as a function of temperature of hydration. Hydrating agents used were aqueous solutions of ammonium chloride, magnesium acetate, magnesium nitrate, nitric acid, acetic acid, magnesium chloride, sodium acetate and hydrochloric acid and distilled water as control. RESULTS: There was not a significant difference in the hydration behavior of the hydrating agents up to 50 °C, where less than 10 % of magnesium hydroxide was formed. The amount of hydroxide increased at temperatures above 60 °C. When compared to the hydration in water, all the hydrating agents with the exception of sodium acetate showed a significant increase in the degree of hydration. Sodium acetate formed the lowest amount of magnesium hydroxide, ranging between 1.2 and 12.2 % magnesium hydroxide. The largest percentage (56.7 %) magnesium hydroxide was formed from the hydration in magnesium acetate. CONCLUSION: It seems that MgO hydration is a dissolution-precipitation process controlled by the dissolution of MgO. The increased degree of hydration in magnesium acetate is possibly due to the presence of acetate and Mg2+ ions.http://www.blackwell-synergy.com

Ammonium sulphate and/or ammonium bisulphate as extracting agents for the recovery of aluminium from ultrafine coal fly ash

We recently showed that the selective extraction of aluminium from the amorphous phase of a South African ultrafine coal fly ash can be achieved via thermochemical treatment with ammonium sulphate for 1 h followed by aqueous dissolution, as an alternative to conventional hydrometallurgical processes. In this study, insight gained from the previous work was applied to investigate and compare total vs selective aluminium extraction efficiencies using ammonium sulphate or ammonium bisulphate either on its own, or as a mixture of the two salts as extracting agents during a 2 h thermal treatment process. The effects of (i) ash-to-extractant mass ratio and (ii) temperature during thermal treatment on extraction efficiency was investigated. While a maximum, but non-selective, recovery of 46.6% total aluminium was achieved using ammonium bisulphate at 400 °C, the most technically appropriate results for selective recovery yielded 37.3% aluminium, with only 0.3% silicon, 0.1% titanium and 3.9% iron having been co-extracted when using ammonium sulphate at a processing temperature of 600°C. Extraction of most of the calcium and magnesium could not be prevented. Using mixtures of ammonium salts as extracting agents during thermochemical treatment may however introduce technical difficulties on large scale. Our results indicate that any of the two ammonium salts could be used on their own during thermochemical treatment. Thermochemical treatment of coal fly ash using ammonium salts may therefore represent a promising technology for extracting aluminium from South African coal fly ash.The Council for Geoscience, the University of Pretoria and the National Research Foundation of South Africa (NRF; Grant No. 93641).http://www.elsevier.com/locate/hydromet2018-08-30hj2017Chemistr