Frans B. Waanders

Galvanic interactions present alternative strategies to achieve a more efficient Cu dissolution from CuFeS₂. The present work studied the interaction between chalcopyrite–magnetite (CuFeS₂-Fe₃O₄) in acidified ferric sulphate Fe₂(SO₄)₃-H₂SO₄ at a solution pH of 1.8 and a temperature of 25 or 50 °C. The addition of Fe₃O₄ to CuFeS₂ forms a galvanic couple, which positively impacts the dissolution of Cu. The results showed that the presence of Fe₃O₄ led to high and fast Cu dissolution rates and decreased significantly the activation energy, from 83 to 57 kJ/mol. In addition to that, the solid residues revealed that CuFeS₂ dissolution produced intermediate Cu-S-rich phases: CuS, Cu₂S and Cu₅FeS₄, which appeared to envelop CuFeS₂, had no observable intermediate phase while in the presence of Fe₃O₄. The results showed that 94% of Cu could be recovered after 5 h of leaching at 50 °C at a Fe₃O₄/CuFeS₂ ratio of 4:1 and a 460 mV Ag/AgCl solution potential. The findings of this study present an option for efficient Cu dissolution from CuFeS₂ in ferric sulphate at atmospheric pressure.

Wastewater treatment has been widely focused on the undesirable pollutants derived from various activities such as coking, coal gasification, oil spills, and petroleum. These activities tend to release organic pollutants, however polycyclic aromatic hydrocarbons (PAHs) happen to be highlighted as the most carcinogenic pollutant that easily comes into contact with the environment and humans. It causes major challenges due to its lingering in the environment and chemical properties. Although various techniques such as ions exchange, advanced oxidation, and reverse osmosis have been conducted, some of them have been ignored due to their cost-effectiveness and ability to produce a by-product. Therefore, there is a need to develop and implement an effective technique that will alleviate the organic pollutants (PAHs) in various water sources. In this study, a self-made flat-bed photoreactor was introduced to degrade PAHs in various water sources such as acidic mine drainage, alkaline mine drainage, and sewage wastewater. A previous study was conducted, and only 7.074 mg/L, 0.3152 mg/L and 1.069 mg/L in 4 weeks and thereafter 19.255 mg/L, 1.615 mg/L and 1.813 mg/L in 8 weeks in acidic mine drainage, alkaline mined, drainage, and sewage wastewater leachate from a 2916.47 mg/L of PAHs in coal tar, was analysed. It was found that the flat-bed photoreactor was highly effective and able to obtain a removal efficiency of 64%, 55%, and 58%, respectively; without the flat-bed photoreactor, happened the removal efficiency was of 53%, 33%, and 39%, respectively, in 60 min in acidic mine drainage, alkaline mine drainage, and sewage wastewater. The photodegradation of PAHs was favoured in the acidic mine drainage, followed by sewage wastewater and alkaline mine drainage respective, showing time and solar irradiation dependence.

Polycyclic aromatic hydrocarbons (PAHs) have been a problem in the environment for an extended period. They are mostly derived from petroleum, coal tar and oil spills that travel and are immobilized in wastewater/water sources. Their presence in the environment causes a hazard to humans due to their toxicity and carcinogenic properties. In the study, coal tar was analyzed using Gas Chromatography–Mass Spectrometry (GC–MS) and a concentration of 787.97 mg/L of naphthalene, followed by 632.15 mg/L of phenanthrene were found to be in the highest concentrations in the various water sources such as sewage, alkaline and acid mine drainage. A design column was used to investigate the leaching process and assessments were conducted on 300 mL of the various water sources mentioned, with 5 g of coal tar added and with monitoring for 4 weeks. The influence of the physiochemical properties of the receiving water sources, such as sewage, and acid and alkaline mine drainage, on the release of PAHs from the coal tar was assessed. The acidic media was proven to have the highest release of PAHs, with a total concentration of 7.1 mg/L of released PAHs, followed by 1.2 mg/L for the sewage, and lastly, 0.32 mg/L for the alkaline mine drainage at room temperature.

The mechanisms involved in the dissolution of chalcopyrite from a carbonatite concentrate in a ferric sulphate solution at pH 1.0, 1.5 and 1.8, and temperatures 25 °C and 50 °C were investigated. Contrary to expectations and thermodynamic predictions according to which low pH would favour high Cu dissolution, the opposite was observed. The dissolution was also highly correlated to the temperature. CuFeS₂ phase dissolution produced intermediate Cu rich phases: CuS, Cu₂S and Cu₅FeS₄, which appeared to envelop CuFeS₂. Thermodynamic prediction revealed CuS to be refractory and could hinder dissolution. CuFeS₂ phase solid-state dissolution process was further discussed. Free Fe₃⁺ and its complexes (Fe(HSO₄)₂⁺, Fe(SO₄)^2– and FeSO₄⁺ were responsible for Cu dissolution, which increased with increasing pH and temperature. The dissolution improved at pH 1.8 rather than 1.0 due to the increase of (Fe(HSO₄)²⁺, Fe(SO₄)^2– and FeSO₄⁺, which were also the predominating species at a higher temperature. The fast and linear first dissolution stage was attributed to the combined effect of Fe³⁺ and its complex (Fe(HSO₄)²⁺, while Fe(SO₄)^2– was the main species for the second Cu dissolution stage characterised by a slow rate.

Due to an ever-changing climate and invasive foreign plant species increase, South Africa struggles with limited water resources. Water is important for the sustenance of all living organisms and it has to be protected. The development of different water treatment techniques becomes more popular to achieve efficient and cost-effective ways of removing contaminants from water. In this study, the property of bentonite clay was altered through impregnation with surfactants such as benzyltrimethylammonium chloride (BTMA), hexadecyltrimethylammonium bromide (HDTM) and tris(hydroxymethyl)aminomethane (THMA) and then used for the removal of the anionic dye, Congo Red (CR), from solutions. The characterization of the different clay samples was done with the use of X-ray diffractometer, X-ray fluorometer and FTIR spectroscopy. To determine the bentonite adsorption affinity the pseudo-first- and second-order kinetic models were used as well as the Langmuir- and Freundlich isotherm models. Other influencing factors that were tested include the effects of adsorbent dosage, initial dye concentration and contact time. The natural bentonite (NB) and bentonite impregnated with BTMA or THMA only adsorbed CR to a certain extent with an adsorption affinity of q_e = 5.00 mg/g, q_e = 1.87 mg/g and q_e = 2.76 mg/g, respectively. The HDTM-impregnated bentonite performed very well in adsorbing CR with an adsorption affinity of q_e = 16.04 mg/g. Evaluation of thermodynamic parameters such as ΔG° and ΔH° indicated that the adsorption process was thermodynamically favourable and endothermic in nature. HDTM can therefore be considered to improve the adsorption capacity of natural bentonite clay for the removal of an anionic dye such as CR.