Quantifying the spreading factor to compare the wetting properties of minerals at molecular level – case study: sphalerite surface

Spreading of water droplet on sphalerite surface was quantified at molecular level and was utilized for comparison of the wetting properties of sphalerite protonated and hydroxylated surfaces. Molecular dynamic simulations were used to characterize the wetting of sphalerite (110) plane. Experimental contact angles of water droplet on sphalerite surfaces were measured and the results were compared with simulated contact angles to ensure that the simulations are accurate enough for calculation of spreading factors. Shape descriptors such as perimeter, area, Feret’s diameters and circularity were used to characterize the shape of droplet-sphalerite interface at molecular level. Using the shape descriptors, different spreading factors were defined and calculated spreading factors were correlated with simulated contact angle. It was shown that spreading factors which were defined as the volume of water droplet divided by the area and Feret’s diameters, with correlation coefficient of 0.98 and 0.97, can be used as accurate tools for wetting comparison of functionalized sphalerite surface at molecular scale. Proposed approach also can be used for investigations on the effect of surface chemical and physical anisotropies on preferred wetting in specific direction at molecular scales

Bubble loading profiles in a flotation column

Bubble loading is the mass of hydrophobic particles attached per unit surface area of air. This measure can be used in the design and analysis of flotation columns as a sign of true flotation. To date, however, this measurement has been limited to the pulp-froth interface, which only indicates the maximum bubble loading and does not reflect the progress of the loading process. This paper introduces the concept of bubble loading profile that summarizes measures of bubble loading at different heights of the collection zone in a flotation column. The effects of bubble size, particle size and collector dosage on the introduced profiles are also investigated. These operational variables changed the bubble loading profile from a linear to a curved trend. The curvatures in the profiles were near the place of the feeding port and therefore the collection zone was divided into two separate zones in terms of bubble loading characteristics. The zone below the feeding port often did not contribute much to the loading of particles on the bubbles and the loading phenomenon mostly took place above the feeding port. Behaviors of the profiles in these two zones were analyzed to reveal that a change in the feeding port placement or column height can, under some conditions, increase the overall bubble loading and thus, ultimately, the true flotation

New Dissolved Nitrogen Predispersed Solvent Extraction Method, 1: Performance

The new Dissolved Nitrogen Predispersed Solvent Extraction (DNPDSE) method was invented for promoting the operational power and improving the equipment performance used in the conventional solvent extraction (SX) method, especially for dilute solutions. The main difference between this method and the SX method is in the mixing mode of aqueous and organic phases. The mixing operation in the SX method is performed with drop dispersion of one phase into another phase; however, in the DNPDSE method, it is carried out with bubble dispersion of organic phase into the aqueous phase. As a result, the performance of the method is improved due to the increase in the contact area of the two phases, thus enhancing in the buoyancy force of the organic phase. The performance comparison of the two methods in similar conditions showed that the copper recovery in the DNPDSE method compared with the SX method in dilute (128 mg Cu/L) and dense (2000 mg Cu/L) synthetic solutions was increased by 22% and 2.5% (on average), respectively

Electrochemical and reactions mechanisms in the minimization of toxic elements transfer from mine-wastes into the ecosystem

The generation of self-protective mine-wastes through a superficial secondary layer to prohibit the leaching of toxic elements can be a new perspective for future environmental studies. The bioleaching-based treatment can lead to the surface passivation of contaminated minerals, which inhibit trace elements mobility. In this work, the electrochemical and passivation mechanisms for the minimization of mine-wastes dissolution were studied on a laboratory scale. The electrochemical behavior of bio-treated soil during surface passivation was investigated by cyclic voltammetry (CV) analysis. The concentration of Fe2+ and Fe3+ in bio-treatment leachates was analyzed to improve our knowledge about the competitive effect of iron ions on the chemical and bacterial dissolution of sulfide tailings. The results of transmission electron microscopy (TEM) and electron probe micro-analyzer (EPMA) confirmed the surface coating of metal sulfides, which led to approximately complete passivation of the minerals. The CV analysis represented that the passivation layer produced in the presence of Acidithiobacillus bacteria was stable in a wide range of redox potential. This study showed that Fe3+ ions play a controlling role in the dissolution process. The high concentration of ferric ions generates a passivation layer in the bulk solution of (bio)leaching. The kinetics study of copper mobility in the minimization process conformed to diffusion control. The results of the kinetics analysis showed that the Cr bioleaching mechanisms followed both the chemical model and diffusion model

Utilization of a Novel Chitosan/Clay/Biochar Nanobiocomposite for Immobilization of Heavy Metals in Acid Soil Environment

An organic–inorganic composite of chitosan, nanoclay, and biochar (named as MTCB) was chosen to develop a bionanocomposite to simultaneously immobilize Cu, Pb, and Zn metal ions within the contaminated soil and water environments. The composite material was structurally and chemically characterized with the XRD, TEM, SEM, BET, and FT-IR techniques. XRD and TEM results revealed that a mixed exfoliated/intercalated morphology was formed upon addition of small amounts of nanoclay (5% by weight). Batch adsorption experiments showed that the adsorption capacity of MTCB for Cu2+, Pb2+, and Zn2+ were much higher than that of the pristine biochar sample (121.5, 336, and 134.6 mg g−1 for Cu2+, Pb2+, and Zn2+, respectively). The adsorption isotherm for Cu2+ and Zn2+ fitted satisfactorily to a Freundlich model while the isotherm of Pb2+ was best represented by a Temkin model. That the adsorption capacity increased with increasing temperature is indicative of the endothermic nature of the adsorption process. According to the FTIR analysis, the main mechanism involved in immobilization of metals is binding with –NH2 groups. Results from this study indicated that modification of biochar by chitosan/clay nanocomposite enhances its potential capacity for immobilization of heavy metals, rendering the bionanocomposite into an efficient heavy metal sorbent in mine-impacted acidic waters and soils