Mining activities are the main cause of generation of the voluminous sludge waste, loaded with metals precipitated from the treatment of acid mine drainage (AMD) and this is always disposed to the landfill. This study aimed at characterizing and suggesting the reusability potential of AMD sludge to reduce the environmental problem caused by its accumulation so that it could become a valuable material. The sludge was obtained after treating a synthetic AMD with a green oxidant sodium ferrate (VI) (Na 2 FeO 4 ) that was prepared by a wet oxidation method. Chemical and physical characterization of a dried sludge generated after treatment was then performed using the Fourier Transform-Infrared and X-Ray powder Diffraction spectroscopy. Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy also served to identify the surface morphology of the sludge. The sludge presented a high weight percentage of Fe and O and lower concentrations of other metals such as Al, Mn, Si, and Na. Nitrogen adsorption/desorption isotherms or Brunauer-Emmett-Teller (BET) was used to assess the surface area, pore volume and diameter of the sludge. The BET results showed that the surface area of the sludge obtained after treating the synthetic AMD using Na 2 FeO 4 was 31.50 ± 0.03 m 2 /g with pore diameter and volume of 52.50 nm and 0.41 cm 3 /g, respectively. However, the produced sludge could serve as an adsorbent to remove pollutants from water or to synthesize different magnetic nanocomposites due to its high surface area (>natural zeolite) and high composition of Fe and O.

The concentration of seven Polycyclic Aromatic Hydrocarbons (PAHs) (namely Naphthalene, Acenaphthylene, Fluorene, Phenanthrene, Anthracene, Pyrene and Chrysene) were determined in 28 surface waters, 8 wastewaters, 26 soils and 26 surface sediments from the Msunduzi River, a major supply of portable water in KwaZulu-Natal (KZN) province, South Africa. Water samples were extracted using a conventional liquid-liquid extraction technique into Dichloromethane (DCM) while soils and surface sediments were extracted with an equal mixture of DCM and nhexane using the Soxhlet extraction technique. Purified extracts were analysed by Gas Chromatography-Mass Spectroscopy (GC-MS). Trace levels of PAHs were detected in some water, river bank soils and surface sediments. The concentration of PAHs was found to be comparatively higher in the soils and surface sediments than in the water. The concentration levels as well as distribution of the selected PAHs varied from season to season, however with no clear pattern. The occurrence pattern of PAHs along the river points to human-related activities as the major input sources of PAHs into Msunduzi water. Paired-up isomeric concentration ratios for surface sediments suggested pyrolysis as the major input source of PAHs, especially at sites closer to the city of Pietermaritzburg (PMB).

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Sodium ferrate solution was prepared by the wet oxidation process using liquid FeCl3 with NaOCl in a strong alkaline solution. The reference and the product were characterized using UV-visible, XRD and FTIR. The maximum concentration of Na2FeO4(VI) solution was 12.4 g/L (as FeO4 2-). Its stability was studied by recording the absorbances of several ferrate solutions at 505 nm on daily basis for a period of one month. The average rates at pH 12 were 3.19 × 10-11 M s-1 for K2FeO4 and 1.09 × 10-11 M s-1 for Na2FeO4. These average rates of degradation indicate that ferrate can last longer without conserving the ferrate solutions using different buffer solutions or phosphates. The peaks obtained around 700, 769 and 879 cm-1 using FTIR confirmed the presence of Fe-O bond in the crystals, which is Na2FeO4 (VI). XRD patterns showed an isomorphism between the diffractograms of Na2FeO4 and K2FeO4.

A major problem in the active treatment of acid mine drainage (AMD) is the generation of large volumes of sludge through pH neutralization, oxidation of iron (II) and subsequent metal precipitation. The sludge settling rate, sludge volume index (SVI) and sedimentation process are ones of parameters identifying a good treatment of AMD. Sodium ferrate (VI) (Na2FeO4) is one reagent currently used to treat water due to its quick reaction rate, easy implementation and relatively low chemical and operational costs. However, very limited information is available in the literature related to the detailed characterization and dewaterability of Na2FeO4-treated AMD sludge. This study aimed at characterizing and monitoring settling rate and densification process of synthetic AMD sludge after treatment with Na2FeO4. The results confirmed a complete removal of iron from the synthetic AMD due to high oxidation strength of ferrate (VI) in acidic medium (Eᵒ = 2.2V) and showed the presence of different minerals formed in the sludge after treatment. The concentrations of the sludge collected at different intervals were justified by the densification process and high density of the sludge was obtained after 25 minutes while high weight percent of iron was found at 10 min and Fe and O dominated other elements in the sludge. The study demonstrated very good settling properties of the sludge and the low SVI value ranging between 30 and 60 mL/g TSS.

Investigation into the production, characterization and application of ferrate(VI) in water and wastewater treatment to enable metal removal through oxidation and coagulation processes and recommended in perspective for AMD treatment as a sustainable process. Revieworganic chemicals, endocrine disrupting chemicals, heavy metals, metal-complexed species, and others in water decontamination processes. Studies also showed that ferrate(VI) salt can be classified as a green chemical which can replace different disinfectants and oxidants producing toxic disinfectant by-products generated by the use of chemicals such as chlorine and chlorine dioxide. Mining industry is another sector, which still has a problem of high energy consumption during acid mine drainage (AMD) treatment. This is due to extensive stirring and aeration which required to facilitate the oxidation of Fe(II) ions. However, the authors recommend the use of ferrate(VI) salt for AMD treatment as it can work as a powerful oxidant converting Fe(II) to Fe(III) and act as a coagulant in a single treating unit, hence, thus reducing energy consumption and environmental pollution problems.

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The screening and treatment of acid mine drainage (AMD) using Na2FeO4 was explored. Elemental composition was performed, using an Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) for the raw and treated AMD. The AMD samples were collected from three different sampling sites:(Raw Tailing Water 1 (RTW1), Raw Tailing Water 2 (RTW2) and Raw Tailing Water 3 (RTW3)) in Pretoria, South Africa, with acidic pH ranging between 2.50 and 3.13. Total dissolved solids and the electrical conductivity of AMD samples ranged between 960 and 1000 mg L−1, 226 and 263 µS. cm−1, respectively. The final pH of treated water samples increased up to ≥9.5 after treatment with sodium ferrate (VI) (Na2FeO4). Liquid Na2FeO4 was quantitatively produced through a wet oxidation method and was fully characterized, using Fourier Transform Infra-Red (FTIR), X-ray Diffraction spectroscopy (XRD) and UV-Vis instruments. Na2FeO4 showed dual functions by removing metals and raising the pH of the treated water. Concentrations of most trace elements did not comply with WHO and DWAF guideline standards in raw AMD while after treatment with Na2FeO4, the concentrations were below guidelines for domestic and irrigation purposes.