Sara J. Couperthwaite

A review of the removal of anions and oxyanions of the halogen elements from aqueous solution by layered double hydroxides

The application of layered double hydroxides (LDHs) and thermally activated LDHs for the removal of various fluorine (F(-),BF4(-)), chlorine (Cl(-),ClO4(-)), bromine (Br(-),BrO3(-)) and iodine (I(-),IO3(-)) species from aqueous solutions has been reviewed in this article. LDHs and thermally activated LDHs were able to significantly reduce the concentration of selected anions in laboratory scale experiments. The M(2+):M(3+) cation ratio of the LDH adsorbent was an important factor which influenced anion uptake. Though LDHs were able to remove some target anion species through anion exchange and surface adsorption thermal activation and reformation generally produced better results. The presence of competing anions including carbonate, phosphate and sulphate had a significant impact on uptake of the target anion as LDHs typically exhibit lower affinity towards monovalent anions compared to anions with multiple charges. The removal of fluoride and perchlorate from aqueous solution by a continuous flow system utilising fixed bed columns packed with LDH adsorbents has also been investigated. The adsorption capacity of the columns at breakpoint was heavily dependent on the flow rate and lower than result reported for the corresponding batch methods. There is still considerable scope for future research on numerous topics summarised in this article.

Effect of strong acids on red mud structural and fluoride adsorption properties.

The removal of fluoride using red mud has been improved by acidifying red mud with hydrochloric, nitric and sulphuric acid. The acidification of red mud causes sodalite and cancrinite phases to dissociate, confirmed by the release of sodium and aluminium into solution as well as the disappearance of sodalite bands and peaks in infrared and X-ray diffraction data. The dissolution of these mineral phases increases the amount of available iron and aluminium oxide/hydroxide sites that are accessible for the adsorption of fluoride. However, concentrated acids have a negative effect on adsorption due to the dissolution of these iron and aluminium oxide/hydroxide sites. The removal of fluoride is dependent on the charge of iron and aluminium oxide/hydroxides on the surface of red mud. Acidifying red mud with hydrochloric, nitric and sulphuric acid resulted in surface sites of the form ≡SOH2(+) and ≡SOH. Optimum removal is obtained when the majority of surface sites are in the form ≡SOH2(+) as the substitution of a fluoride ion does not cause a significant increase in pH. This investigation shows the importance of having a low and consistent pH for the removal of fluoride from aqueous solutions using red mud.

Adsorption of reactive dye on seawater-neutralised bauxite refinery residue.

This investigation has demonstrated the need for thermal treatment of seawater neutralised red mud (SWRM) in order to obtain reasonable adsorption of Reactive Blue dye 19 (RB 19). Thermal treatment results in a greater surface area, which results in an increased adsorption capacity due to more available adsorption sites. Adsorption of RB 19 has been found to be best achieved in acidic conditions using SWNRM400 (heated to 400°C) with an adsorption capacity of 416.7 mg/g compared to 250.0mg/g for untreated SWNRM. Kinetic studies indicate a pseudosecond-order reaction mechanism is responsible for the adsorption of RB 19 using SWNRM, which indicates adsorption occurs by electrostatic interactions.

Enhanced water recovery in the coal seam gas industry using a dual reverse osmosis system

Mining of brines produced in the coal seam gas industry for water and salts is of major concern globally. This study focussed on the use of a dual stage reverse osmosis system to achieve high water recovery rates. It was our hypothesis that an intermediate nanofiltration stage was required to stabilize the performance of the second reverse osmosis stage. The second stage RO membrane was found to be fouled by silica and aluminosilicates when used with any intermediate brine treatment. Theoretical predictions using PHREEQC software supported the experimental outcomes in terms of identifying species with high scaling potential. Coagulation of the coal seam brine using aluminium chlorohydrate was found to remove up to 70.5% of dissolved silica and thus this method may be useful for prevention of fouling of downstream membranes. ROSA software was also employed to enable selection of possible nanofiltration membranes to treat the coal seam brine sample. Tighter membranes were found to exhibit significantly higher rejection of ions responsible for scale formation during brine concentration operations. Albeit, the flux rates were less than the looser membrane types. A pressure of 20 bar was suggested to be practical for the nanofiltration stage as the flux rate more than doubled from the flux estimated at 15 bar. An intermediate nanofiltration stage perhaps combined with a coagulation step is recommended for use in a dual stage RO system to concentrate coal seam brines.

A Raman spectroscopic study of the basic carbonate mineral callaghanite Cu2Mg2(CO3)(OH)6·2H2O.

Raman spectrum of callaghanite, Cu2Mg2(CO3)(OH)6·2H2O, was studied and compared with published Raman spectra of azurite, malachite and hydromagnesite. Stretching and bending vibrations of carbonate and hydroxyl units and water molecules were tentatively assigned. Approximate O-H…O hydrogen bond lengths were inferred from the spectra. Because of the high content of hydroxyl ions in the crystal structure in comparison with low content of carbonate units, callaghanite should be better classified as a carbonatohydroxide than a hydroxycarbonate.

Vibrational Spectroscopy of the Multianion Mineral Kemmlitzite (Sr,Ce)Al3(AsO4)(SO4)(OH)6

ABSTRACT Some minerals are colloidal and show no X-ray diffraction patterns. Vibrational spectroscopy offers one of the few methods for the assessment of the structure of these types of minerals. Among this group of minerals is kemmlitzite (Sr,Ce)Al3(AsO4)(SO4)(OH)6. The objective of this research is to determine the molecular structure of the mineral kemmlitzite using vibrational spectroscopy. Raman microscopy offers a useful method for the analysis of such colloidal minerals. Raman and infrared bands are attributed to the , , and water stretching vibrations. The Raman spectrum is dominated by a very intense sharp band at 984 cm−1 assigned to the symmetric stretching mode. Raman bands at 690, 772, and 825 cm−1 may be assigned to the antisymmetric and symmetric stretching modes. Raman bands observed at 432 and 465 cm−1 are attributable to the doubly degenerate ν2(SO4)2− bending mode. Vibrational spectroscopy is important in the assessment of the molecular structure of the kemmlitzite, especially when the mineral is nondiffracting or poorly diffracting.

Vibrational spectroscopic study of multianion mineral clinotyrolite Ca2Cu9[(As,S)O4]4(OH)10·10(H2O)

The molecular structure of the mixed anion mineral clinotyrolite Ca(2)Cu(9)[(As,S)O(4)](4)(OH)(10)·10(H(2)O) has been determined by the combination of Raman and infrared spectroscopy. Characteristic bands associated with arsenate, sulphate and hydroxyl units are identified. Broad bands in the OH stretching region are observed and are resolved into component bands. Estimates of hydrogen bond distances were made using a Libowitzky function and both short and long hydrogen bonds are identified. Two intense Raman bands at 842 and ∼796 cm(-1) are assigned to the ν(1) (AsO(4))(3-) symmetric stretching and ν(3) (AsO(4))(3-) antisymmetric stretching modes. The comparatively sharp Raman band at 980 cm(-1) is assigned to the ν(1) (SO(4))(2-) symmetric stretching mode and a broad Raman spectral profile centred upon 1100 cm(-1) is attributed to the ν(3) (SO(4))(2-) antisymmetric stretching mode.