Studies on Curcumin Loaded Poly(N-isopropylacrylamide) Silver Nanocomposite Hydrogels for Antibacterial and Drug Releasing Applications

Design of silver nanoparticles containing poly(N-isopropylarclamide) (PNIPAAm) hydrogels were prepared by free-radical polymerization of N-isopropylarclamide as an environmentally sensitive monomer and MBA as a crosslinker in an aqueous medium. The embedded silver nanocomposite hydrogels (AgNCH) structure were characterized by, UV-Vis, FTIR, DLS, TEM and X-ray analysis. Curcumin loading and release characteristics were performed for PNIPAAm hydrogel, silver ions loaded hydrogels as well as silver nanocomposite hydrogels. These curcumin loaded silver nanocomposite hydrogels exhibit excellent antibacterial action on Escherichia coli (E. coli). Therefore, the present study clearly provides novel antimicrobial hydrogels which are potentially useful in biomedical applications.     

Mössbauer spectroscopy study of mechanically alloyed Fe2O3–(Al, Co and WC) systems

Mössbauer spectroscopy revealed that a central hyperfine interaction doublet and an additional sextet characterized the appearance of new phases in the mechanically alloyed Fe₂O₃–Al and Fe₂O₃–Co systems. In the Fe₂O₃–Al system, the intensity of the central super paramagnetic doublet which represents small particles of iron, increased with increasing milling time from 5 to 30 h of mechanical alloying. The magnetic sextet characterizing hematite vanished in the room temperature Mössbauer spectra of samples produced after 25 h of mechanically alloying the 50% Fe₂O₃ and 50% Al system. In general XRD peak broadening was observed as a result of extensive material structural distortion and formation of small particles. Fe, Al₂O₃ and mixed iron–aluminium oxide phases were identified in the XRD patterns with a small persistence of the iron oxide up to 20 h of mechanically alloying the 1:1 system Al–Fe₂O₃. In the 50% Co–50% Fe₂O₃ system, a 55% abundant new phase CoFe₂O₄ was observed, from the Mössbauer spectra of the system. The presence of this new phase was confirmed by the XRD analysis. The high energy ball milling of WC–Fe₂O₃ revealed a more effective grinding compared to hematite alone. The hematite particles were reduced to nanosized particles.     

Hydrometallurgical Extraction of Zinc and Copper – A 57Fe-Mössbauer and XRD Approach

The most commonly used route in the hydrometallurgical extraction of zinc and copper from a sulphide ore is the concentrate–roast–leach–electro winning process. In the present investigation a zinc–copper ore from the Maranda mine, located in the Murchison Greenstone Belt, South Africa, containing sphalerite (ZnS) and chalcopyrite (CuFeS₂), was studied. The ⁵⁷Fe-Mössbauer spectrum of the concentrate yielded pyrite, chalcopyrite and clinochlore, consistent with XRD data. Optimal roasting conditions were found to be 900°C for 3 h and the calcine produced contained according to X-ray diffractometry equal amounts of franklinite (ZnFe₂O₄) and zinc oxide (ZnO) and half the amount of willemite (Zn₂SiO₄). The Mössbauer spectrum showed predominantly franklinite (59%), hematite (6%) and other Zn- or Cu-depleted ferrites (35%). The latter could not be detected by XRD analyses as peak overlapping with other species occurred. Leaching was done with HCl, H₂SO₄ and HNO₃, to determine which process would result in maximum recovery of Zn and Cu. More than 80% of both were recovered by using either one of the three techniques. From the residue of the leaching, the Fe-compounds were precipitated and <1% of the Zn and Cu was not recovered.     

The South African industry use of Mössbauer spectroscopy to solve operational problems

South Africa is a country that is very rich in mineral resources but the use of Mössbauer spectroscopy to solve operational industrial problems is however very limited. In the Bushveld Igneous Complex the main minerals extracted from the ore are the platinum group metals and chromium, but secondary recovery of base metals such as nickel, copper and cobalt forms an integral part of the process. Losses of nickel in the slag can amount to about 4 % and subsequent a slag cleaning furnace is used to reduce the loss to less than 0.5 % nickel oxide. The Fe²⁺/Fe³⁺ ratio and mineralogy was used to determine the partial oxygen pressure in the furnaces and also the efficiency of the nickel recovery. From the Mössbauer results, augmented with XRD, SEM, EMP-WDX and MLA analyses, optimum conditions were determined to ensure minimum metal losses. The use of Mössbauer spectroscopy in the coal industry, to investigate mineral changes that occur during its use, is also of importance. The main minerals present in coal were determined with the aid of various techniques, such as Mössbauer, XRD, SEM and HR-TEM, with the major iron minerals found to be pyrite, illite, ankerite and jarosite. A large quantity of coal is used to produce syngas via gasification plants for the production of synthetic fuels. The change of the mineral matter during gasification was studied and the changes occurring during the gasification process were followed. The syngas produced, is further treated by means of the Fischer–Tropsch process where an iron catalyst is incorporated in the process. The usefulness and fouling of the catalyst is being studied with the aid of Mössbauer spectroscopy. The calibration of equipment to determine work hardening in mining equipment was also investigated and found to be a useful tool in industry. From the above few examples it is evident that, although used on a limited base, Mössbauer spectroscopy, augmented by various other spectroscopic tools, still ensures optimal recovery and production of the vast resource base of South Africa.     

Iron in reduced charge montmorillonites

Reduced charge Camp-Berteau Montmorillonites (R.C.M.) have been studied. The Cation Exchange Capacity (C.E.C.) resulting from these samples with different Li/Na ratios decreased linearly from the original value of about 1 meq/g to 0.6 meq/g. Diffused Li⁺ ended in octahedral layer nearby Mg²⁺. Iron was as Fe³⁺ and mainly in octahedral sites. A small additional quantity of tetrahedral configuration was detected. Only minor modifications on Mössbauer parameters of R.C.M. samples were observed as a consequence of charge reduction.     

Mössbauer spectroscopy of exchangeable ions

In this paper Mössbauer spectroscopy is used to study anion exchange processes. In β-FeOOH the effect of the exchangeable ions OH^?, Cl^? and F^? on lattice iron is studied. For the anion exchangers ZrO₂ and the resins amberlite IRA 400, Dowex MSA-1 and Dowex MWA-1, Fe(II)- and Fe(III) hexacyanides are used as Mössbauer probes. The confirmation of a third doublet in F^?-exchanged β-FeOOH and the perturbation of redox equilibrium in the other exchangers are the main observations.     

57 Fe Mössbauer and X-ray characterisation of sandstones

Sandstones from the Free State province in South Africa have been mined and processed mainly by small scale and artisanal miners in the rural areas. In the present investigation basic fire proof and water absorption tests, X-ray and γ-ray based characterisation techniques were used to study the sandstones. The collected samples were grouped according to their apparent colour in day light conditions and the elemental analysis showed the presence of a high amount of oxygen (>52%) and silicon (>38%) with Mn, Al, Fe and Ca as major elements in proportions related to the colour distribution of the various sandstones. The uniaxial compressive stress was found to be the highest (56 MPa) for the greyish sandstone and the lowest (8 MPa) for the white sandstone sample, also associated with the lowest (Al+Fe)/Si value of 0.082. The humidity test showed that the 6 % water absorption was lower than the recommended ASTM value of 8 %. The sandstone samples were also subjected to various high temperatures to simulate possible fire conditions and it was found that the non alteration of the mineral species might be one of the reasons why the sandstones are regarded as the most refractory amongst the building materials typically used. Mössbauer spectroscopy revealed that iron is present in all the sandstones, mainly as Fe^3?+? with the black sandstone showing an additional presence of 3 % Fe^2?+? indicating that a higher iron content coupled to higher silicon content, contributes to an increase in the uniaxial compressive strength.     

Ilmenite Mineral's Recovery from Beach Sand Tailings

The mineral ilmenite is the major source of rutile for industrial use and is of interest to paint and fertiliser industries. Enormous unutilised tailing dams lie on the eastern coast of the South Africa. Although covered by a simulation of the original indigenous vegetation, these tailings are still ilmenite bearing and of economic value. Tailings emanating from beach sand mineral slimes dams of the Kwazulu-Natal area (South Africa) have been processed. Screening, flotation, spiral concentration and magnetic separation methods were used either separately or successively. The present work sheds light on alternative routes for the extraction of the ilmenite, from these tailings. It moreover points out the usefulness of the Mössbauer spectroscopy in the mineral processing product monitoring. Tailings from the beach sands were used in the present study after the economic industrial minerals zirconia, ilmenite and rutile had been extracted in previous mining operations. About 61% natural ilmenite recovery was observed in the flotation concentrate of a Humphrey Spiral concentrate while a 62% recovery of hematite was found in the flotation tailings. The combination of screening, spiral concentration and magnetic separation, and flotation yielded a product with the highest ilmenite and hematite concentration being 71% and 19%, respectively. A natural ilmenite mineral, containing 87% ilmenite and 13% hematite, could be produced and extracted from the tailings of the flotation process, collected subsequently to the spiral concentration and the initial screening.     

Retained Austenite Phase in (26.5%Cr, 2.6%C) White Cast Iron Studied by Means of CEMS and Eddy Current

High chrome white irons are specifically employed in the mining industry for their resistance to wear. More cost-effective materials are constantly being sought, due to the high wear rate of the drilling components, which is a high cost area for this industry. Optimum resistance to wear is often not the main criterion of material selection but parameters such as ease of fabrication; availability and low initial cost have also to be accounted for. A correctly heat-treated high chrome white iron of a right chemical composition presents the best hardness and toughness combination [1]. A (26.5 wt.% Cr, 2.6 wt.% C) white iron has been produced by casting and heat-treating. As the retained austenite phase has the ability to harden, the control of its content may result in tuning the applications of this material. Various heat-treatments were given to the above-mentioned material to achieve a spread of austenite values. The retained austenite phase amount was measured by means of X-ray diffraction (XRD), Conversion Electron Mössbauer spectroscopy (CEMS) and Eddy current techniques. A linear correlation between results from Eddy Current and CEMS, Eddy-current and XRD, and between those from CEMS and XRD was observed. As the nominal abundance values were technique dependent, their conversion will be discussed. The present study results in the calibration of the Eddy current apparatus and suggests its application in the casting industry during mass production for the retained austenite content determination in high chrome white iron castings.     

Characterization of products emanating from conventional and microwave energy roasting of chalcopyrite (CuFeS2) concentrate

Chalcopyrite concentrate (83% CuFeS₂, 3% FeS₂ and 14% ZnS) which is a typical feed to the matte smelting process for copper extraction via pyro metallurgical route has been roasted with microwaves. Comparison of mineralogical phases obtained was made with the case of conventional roasting. Resulting calcines were characterised with Mössbauer spectroscopy and XRD. It was observed that complete oxidation (dead roasting) of the chalcopyrite was achieved after 10 min with microwaves while 20 min were required in the conventional route. The mineralogical phases found in the dead-roasted calcines produced from microwave roasting of this chalcopyrite concentrate were the hematite (Fe₂O₃), franklinite (ZnFe₂O₄), copper-rich ferrite (Cu_1?x Zn _x Fe₂O₄, x?≤?0.5), and copper ferrite (CuFe₂O₄). The findings of this work indicated that it was technologically feasible to oxidize the chalcopyrite with microwaves using a 2.45 GHz multimode applicator.