Comparative study of two biggest mineral wastes in South Africa for mine reclamation: A geotechnical study

Abstract : Laboratory investigations were conducted on two mineral wastes to assess their geotechnical properties for mine backfilling. Composite Coal Fly Ash (CFA) sludge recovered from CFA and acid mine drainage (AMD) reaction (ratios 1:2 and 1:3) and gold mine tailings (GMT) with 3 % cement were evaluated at varying curing ages. Both samples showed favourable characteristics for use in mine reclamation. However, solid/liquid ratios should be maintained to ensure maximum strength. The results show that CFA can be recommended for mine reclamation due to it geotechnical properties. The use of GMT is possible, however blending with higher percentages of cement should be considered

Evaluation of South African gold tailings as a mine backfilling material

Abstract : This paper presents the results of laboratory investigations conducted on gold mine tailings (GMT) to assess their chemical, mineralogical, leaching and geotechnical characteristics as well their acid generating potential in view of assessing its suitability as an alternative backfilling solution in mine reclamation. Chemical characterisation revealed that GMT is dominated by Si, Al and Fe with notable amounts of Cr, Zr, Zn, Pb, Ce, As, Ba, Ni, V, Sr, Nd, Cu, U and Co. Mineralogical characterisation revealed a composition of silicate minerals with secondary minerals such as jarosite, goethite and hematite. Acid base accounting (ABA) results showed that GMT are acid generating. During column leach experiments, leaching of elements and SO42- was significant at initial stages and became negligible thereafter. GMT composites exhibited moderate strength parameters. The effect of curing age and addition of cement contributed to the shear strength of the material. Furthermore, GMT showed favourable characteristics for use in mine backfilling; however, solid/liquid ratios should be maintained to ensure maximum strength. The use of GMT for backfilling is therefore possible; however, blending with higher percentages of cement and alkaline materials such as coal fly ash should be considered to chemically stabilise the material

Amending the anisotropy barrier and luminescence behavior of heterometallic trinuclear linear M-II-Ln(III)-M-II (Ln(III)=Gd, Tb, Dy; M-II=Mg/Zn) complexes by change from divalent paramagnetic to diamagnetic metal ions

The sequential reaction of a multisite coordinating compartmental ligand LH4 [2-(2-hydroxy-3-(hydroxymethyl)-5-methylbenzylideneamino)-2-methylpropane-1,3-diol] with appropriate lanthanide salts followed by the addition of Mg(NO3)2·6H2O or Zn(NO3)2·6H2O in a 4:1:2 stoichiometric ratio in the presence of triethylamine affords a series of isostructural heterometallic trinuclear complexes containing [Mg2Ln]3+ [Ln = Dy (1), Gd (2) and Tb (3)] and [Zn2Ln]3+ [Ln = Dy (4), Gd (5) and Tb (6)] cores. The formation of 1-6 is demonstrated by X-ray crystallography as well as ESI-MS spectra. All complexes are isostructural possessing a linear trimetallic core with a central lanthanide ion. In this article we have discussed the comprehensive studies, involving synthesis, structure, magnetism and photophysical properties on this family of trinuclear [Mg2Ln]3+ and [Zn2Ln]3+ heterometallic complexes. Complexes 1 and 4 show slow relaxation of the magnetization below 12 K under zero applied direct-current field, but without reaching a neat maximum which is due to the overlapping with a faster quantum tunnelling relaxation mediated through dipole-dipole and hyperfine interactions. Under a small applied direct-current field of 1000 Oe the quantum tunneling was almost suppressed and temperature and frequency dependent peaks were observed, thus confirming the SMM behavior of complexes 1 and 4. The fit of the high-temperature relaxation times to the Arrhenius equation affords an effective energy barrier for the reversal of the magnetization of Ueff =72(2) K with o = 8 x 10-9 s for the SR process and Ueff = 61(2) K with o = 4 x 10-7 s for the FR process for 1 whereas for 4, an effective energy barrier for the reversal of the magnetization Ueff = 67(3) K with o = 4.5 x 10-8 s. To rule out the involvement of intermolecular collaborative interactions in the dynamic of relaxation, we have performed ac susceptibility measurements on 1:10 Dy:Y magnetic diluted samples of of 1 and 4, named as 1' and 4'. Interestingly, the diluted compounds 1' and 4' exhibits SMM behavior under zero magnetic field, thus suggesting that their relaxation processes are single molecular in origin and arise from the M-Dy-M unit. Ab initio CASSCF+RASSI calculations carried out on 1 and 4 confirm that the magnetic anisotropy is axial along the M-Dy-M axis and that the relaxation process occurs through the first excited energy level. Furthermore, the chromophoric [LH3]2- ligand is able to act as an 'antenna' group which was found to be effective in the selective sensitization of the emissions of TbIII-based complexes 3 and 6. The emission quantum yields and the luminescence lifetimes at room temperature are 11.7 % and 0.606 ms for 3, 22.7 % and 0.799 ms for 6

A GPU implementation of a track-repeating algorithm for proton radiotherapy dose calculations

An essential component in proton radiotherapy is the algorithm to calculate the radiation dose to be delivered to the patient. The most common dose algorithms are fast but they are approximate analytical approaches. However their level of accuracy is not always satisfactory, especially for heterogeneous anatomic areas, like the thorax. Monte Carlo techniques provide superior accuracy, however, they often require large computation resources, which render them impractical for routine clinical use. Track-repeating algorithms, for example the Fast Dose Calculator, have shown promise for achieving the accuracy of Monte Carlo simulations for proton radiotherapy dose calculations in a fraction of the computation time. We report on the implementation of the Fast Dose Calculator for proton radiotherapy on a card equipped with graphics processor units (GPU) rather than a central processing unit architecture. This implementation reproduces the full Monte Carlo and CPU-based track-repeating dose calculations within 2%, while achieving a statistical uncertainty of 2% in less than one minute utilizing one single GPU card, which should allow real-time accurate dose calculations

Competition between terminating and collective structures above spin 40ℏ in 154Dy

High-spin states in 154Dy were studied with the Gammasphere spectrometer using the 36S(122Sn,4n) reaction. Band terminating states were identified in the spin range I= (36-48)ℏ, and were found to compete with collective rotational cascades up to the highest observed spins. Several "sidebands" feeding the terminating structures were identified as well. A band dominated by M1 transitions was observed to terminate at Iπ = 42-. The data are interpreted within the framework of configuration-dependent cranked Nilsson-Strutinsky calculations without pairing

Effect of fly ash size fraction on the potential to neutralise acid mine drainage and rheological properties of sludge

Large quantities of fly ash (FA) are generated annually in South Africa and most of it is disposed in landfills and ash dams. Previous studies indicated that FA can be used to treat acid mine drainage (AMD), another waste stream commonly found in the minerals industry. Moreover, encouraging results were obtained from the studies carried out on the sludge (referred as solid residues (SR) hereafter) recovered from FA-AMD treatment as a suitable mine backfill material. Particle size distribution (PSD) of FA plays an important role in the AMD treatment quality and viscosity of the SR that can be used directly for backfill purposes. In this study, we have investigated the effect of PSD of FA on AMD neutralisation and metal removal. This work also looked at the effect of PSD on the rheology of the SR. Neutralisation experiments indicated that the higher fines fraction enhances the treatment of AMD by reducing the time taken to increase the pH to a minimum of 7. Moreover, FA with higher fines fraction has reduced the Mn and levels better than the normal and higher coarse fraction FA. X-ray fluorescence analysis on SR confirmed the metal removal trends observed during the neutralisation experiments. Laboratory scale studies were carried out on the rheology of SR using a rheometer. It was found that increasing the coarse fraction results in higher viscosity than by increasing the fines fraction. The observed behaviour is contrary to the notion that increase in fines fraction will increase the viscosity of the suspension. This study shows that there may be some truth in the controversial effect of coarse particles on the rheology of suspensions

An innovative impression technique for fabrication of a custom made ocular prosthesis

Various impression and fitting techniques have been described in the past for restoring ocular defects. The present article describes a new direct impression technique for recording and rehabilitating ocular defects, by custom-made ocular prosthesis. All the techniques described in the history, mainly concentrated in recording the tissue surface of the defect, which made it difficult to contour the palpebral surface resulting in the poor esthetics of the prosthesis. The present impression technique uses heavy bodied polyvinyl siloxane impression material, which facilitates accurate recording of the tissue surface and the palpebral surface of the defect, resulting in the fabrication of functionally and esthetically acceptable prosthesis