Potential low-cost carbon-based adsorbent from gold mine tailings for anionic dye removal.

In this study, a mesoporous carbon (CMK-3) was successfully synthesized using mesoporous silica (SBA-15) prepared from gold mine tailings (sample CGMT) for removal of anionic dye from aqueous solution. For comparison, CMK-3 was prepared by the same method from pure silica (sample CT), and the other CMK-3 sample was prepared by a one-pot route mixing with Pluronic P123 (sample CP). The effect of the carbonization time on the synthesis of all CMK-3 samples was investigated, and the samples were characterized by X-ray diffraction and N2 adsorption-desorption. The sample with the highest surface area was chosen as an adsorbent, for each CMK-3 obtained from different methods. Batch adsorption experiments were studied to determine the influence of pH, contact time, and initial dye concentration. The adsorption kinetics obeyed the pseudo-second-order model. All carbon-based adsorbents were observed to be quite effective for the removal of dye with adsorption percentage in the order of CP > CT > CGMT. The maximum adsorption capacities were 188.99 and 204.57 mg·g-1 for CT and CGMT, respectively. The comparative results of all carbon-based adsorbents show that CGMT can be applied as a low-cost alternative to CT for dye removal.

Dual antimicrobial effects induced by hydrogel incorporated with UV-curable quaternary ammonium polyethyleneimine and AgNO3.

This study presents a simple method for fabricating a highly potent dual effect antibacterial hydrogel consisting of a UV-curable cationic polyethyleneimine (QUV-PEI) and embedded silver nitrate (AgNO3). In the first part of this study, polyethyleneimine (PEI) was reacted with 3-(acryloyloxy)-2-hydroxypropyl methacrylate (ACOM) to introduce methacryl functionality onto the backbone. UV-curable PEI was further quaternized by N-methylation with methyl iodate. Hydrogels based on QUV-PEI and AgNO3were found to have impressive biocidal properties. The antibacterial properties were assessed by spraying aqueous suspensions of bacterial cells on the surface, followed by air drying and counting the number of remaining viable cells (i.e. capable of growing into colonies). In a manner depending on the QUV-PEI content in the gel formulation, up to 99±1% of Escherichia coli and Staphylococcus aureus cells sprayed on the resulting hydrogel surfaces were killed. The inclusion of AgNO3 in the QUV-PEI based hydrogel not only enhanced the antimicrobial property against adherent bacteria but also led to the inhibition of bacterial growth in suspended culture via the long-term release of Ag/Ag(+) to the surrounding media. Cytotoxicity studies on human umbilical vein endothelial cells and MTS cell lines were also performed with hydrogels. These findings confirm that hydrogels are potentially useful as antimicrobial agents in a wide variety of applications.

Utilization of gold tailings as an additive in Portland cement.

Mine tailings are formed as an industrial waste during coal and ore mining and processing. In the investigated process, following the extraction of gold from the ore, the remaining tailings are subjected to a two-stage chemical treatment in order to destroy the free cyanide and to stabilize and coagulate heavy metals prior to discharge into the tailings pond. The aim of this study was the investigation of the feasibility of utilization of the tailings as an additive material in Portland cement production. For this purpose, the effects of the tailings on the compressive strength properties of the ordinary Portland cement were investigated. Chemical and physical properties, mineralogical composition, particle size distribution and microstructure of the tailings were determined by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), particle size analyzer (Mastersizer) and scanning electron microscope (SEM). Following the characterization of the tailings, cement mortars were prepared by intergrinding Portland cement with dried tailings. Composition of the cement clinkers were adjusted to contain 5, 15, 25% (wt/wt) dried tailings and also silica fume and fly ash samples (C and F type) were added to clinker in different ratios. The mortars produced with different amounts of tailings, silica fume, fly ashes and also mixtures of them were tested for compressive strength values after 2, 7, 28 and 56 days according to the European Standard (EN 196-1). The results indicated that gold tailings up to 25% in clinker could be beneficially used as an additive in Portland cement production. It is suggested that the gold tailings used in the cement are blended with silica fume and C-type fly ash to obtain higher compressive strength values.

Kinetic study of the thermal dehydration of borogypsum.

In Turkey, a large amount of borogypsum waste is discharged by the economically important boric acid industry. Calcination of this waste provides a promising technique not only for recovering an economic value but also for reducing its environmental impact. The aim of this work is to study the thermal behavior of borogypsum, which contains gypsum crystals, boron oxide and some impurities under nonisothermal conditions in air atmosphere by using thermogravimetry and differential thermal analysis techniques (TG-DTA). Experiments were carried out at temperatures ranging from ambient to 773 K at different heating rates. The temperatures of conversion from gypsum to hemihydrate and anhydrite states were determined. Various methods were used to analyze the TG and DTA data for determination of reaction kinetics. The activation energy and frequency factor were calculated for dehydration of borogypsum. Activation energy values of the main dehydration reaction of borogypsum were calculated to be approximately 95-114 kJ mol(-1).