Fine particles in the presence of flotation reagents exhibit different dispersion and aggregation behaviors in a mineral suspension, and affect the flotation separation processes. In this study, the effects of three quaternary ammonium salts (i.e., dodecyltrimethylammonium chloride (DTAC), tetradecyltrimethylammonium chloride (TTAC), and hexadecyltrimethylammonium chloride (CTAC)) on the dispersion and aggregation behaviors of kaolinite and quartz were studied. The mechanism was systematically investigated using sedimentation tests, reagent adsorption analysis, zeta potential measurements, and SEM analysis. In the absence of reagents, the kaolinite and quartz particles exhibited good aggregation behaviors at acid and neutral pHs compared with alkaline conditions. Except for CTAC, the presence of DTAC and TTAC improved the aggregation behavior of both minerals in neutral and alkaline conditions. More, the sedimentation yields of both minerals were increased significantly with increasing the concentration of DTAC and TTAC. However, the increasing concentration of CTAC resulted in an increase in the dispersion of kaolinite and quartz particles under the same conditions. At neutral and alkaline conditions, the zeta potentials and adsorbed amounts of all three salts on the mineral surfaces were increased significantly with increasing the concentrations of salts, and the adsorbed amount adopted the following sequence: CTAC > TTAC > DTAC. The zeta potential results showed that the stronger adsorption of quaternary ammonium salts on mineral surfaces at neutral and alkaline conditions was mainly because of electrostatic interactions.

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In the field of water management, the separation of metal contaminants from wastewater is very important and challenging. This study systematically investigated the effect and underlying mechanism of silicate rectorite (REC) on the removal of heavy metal ions (Cr(VI) and Pb(II)) from wastewater. The adsorption and removal capacity of REC was further improved by its novel modification with ferric chloride hexahydrate. Compared to natural REC, the modified rectorite (Fe-REC) showed comparatively superior adsorption efficiency for both Cr(VI) and Pb(II) due to the chemisorption of Fe 3+ on the REC surface as its oxidation state (Fe-O, Fe-OH, Fe-OOH). Adsorption on Cr(VI) attributed to the reaction between iron hydroxy complexes (FeOH 2+ , Fe(OH) 2 + and Fe(OH) 3 (aq)) and Cr(VI) species (HCrO 4 − and CrO 4 2− ) in the aqueous solution. This reaction was perfectly consistent with the binding energy shifts in O 1s and Fe 2p species, as reflected by XPS analysis. While, the existence of -Al-OH and -Si-OH in silicate REC slurry reacted with PbOH + colloids produced from lead ions hydrolysis to promote Pb(II) adsorption. Zeta potential after modification and removal occurred to shift positively or negatively to testify the adsorption of Fe 3+ and heavy metal ions. Freundlich and Langmuir isotherms conformed adsorption process for Cr(VI) and Pb(II), respectively.Minerals 2020, 10, 176 2 of 16 and economical approach that is widely used in wastewater treatment procedures. In adsorption, a variety of adsorbent including activated carbons, clay mineral, biomasses and synthetic polymers was employed [8,[10][11][12][13]. However, common adsorbents such as activated carbon are expensive, thus some natural resources such as polysaccharides, fly ash and clay have attracted much attention due to their low cost and easy access. In this series of materials, rectorite (REC) was applied more and more in pollutant adsorption from sewage owing to its low cost, high ion exchange capacity and relatively large specific area [14][15][16][17]. It is a sort of rare regularly interstratified silicate and similar to kaolinite. Its special structure is alternate pairs of dioctahedral mica-like layer (non-expansible) and dioctahedral smectite-like layer (expansible) existing in 1:1 ratio. There are some cations (Na + , K + and Ca 2+ ) and hydrated cations with exchangeability, which can enlarge its interlayer distance by intercalating cations or polar molecules existing in the interlayer regions.Over several decades, there are more and more investigations on the adsorption of metal ions by REC or its synthesis [17][18][19][20][21]. For example, Mei et al. [17] and Zhao et al. [22] studied separately the adsorption behaviors of Pb(II) by Ca-rectorite and Sr(II) by Na-rectorite as a function of different environmental parameters including the influence of pH, temperature, ionic strength and humic acid (HA) under ambient conditions. Both of them found that the adsorption results of heavy metals were intensely decided by pH and ionic strength and the...

Contact angle measurement is very important in determining the liquid-solid affinity properties of materials. In recent years, many advances have been made in the research of contact angle automatic measurement algorithms, but most of the existing image processing and analysis algorithms are very sensitive to changes in the characteristics of the target, including the light source illumination angle, brightness, and the tangent of the camera lens axis to the target point Factors such as error will affect the measured contact angle. This paper proposes a key improvement technique, using the MOG background subtraction technology to realize that only the edge of the morphology after the final stabilization of the droplet is reduced, which reduces the serious interference of the mirror image of the droplet on the smooth material surface on the measured value. This method has achieved accurate fitting of the droplet contour circle, avoiding the use of measurement parameters with large errors to calculate. The algorithm has many advantages, in particular, it has noise resistance to changes in the shape, size and position of the sample, has good robustness, and has low calculation cost and fast speed. The measurement results are very similar to the manual marking of manual optical measurement High consistency.

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