Roles and Influences of Kerosene on Chalcopyrite Flotation in MgCl2 Solution: EDLVO and DFT Approaches

Seawater has been increasingly used as an alternative to freshwater in mineral flotation. Although previous studies suggest that Mg2+ ions in seawater have the primary negative roles in chalcopyrite flotation, insufficient work has been conducted to understand the effects of kerosene as a collector in chalcopyrite flotation. In this study, the influence of kerosene emulsion on chalcopyrite floatability in a solution containing Mg2+ was systematically investigated. The results indicated that the addition of kerosene significantly reduced the adsorption of hydrophilic Mg-precipitates onto the chalcopyrite’s surface. In addition to contact angle, zeta potential, optical microscopy, and Fourier-transform infrared spectroscopy analyses, extended Derjguin–Landau–Verwey–Overbeek (EDLVO) theory and density functional theory (DFT) calculations were conducted to understand the influencing mechanisms of kerosene on chalcopyrite flotation. The adsorption energies showed an order of kerosene and Mg(OH)2 > kerosene and chalcopyrite > chalcopyrite and Mg(OH)2, indicating kerosene was preferentially adsorbed on the Mg(OH)2 surface, forming agglomerates and therefore reducing the adsorption of Mg(OH)2 precipitates onto the chalcopyrite’s surface. In addition, hydrophobic agglomerates were also formed due to the attachment of kerosene to the chalcopyrite’s surface when additional kerosene was added, further enhancing chalcopyrite floatability.

Electrochemical Deposition Treatment (EDT) as a Comprehensive Rehabilitation Method for Corrosion-Induced Deterioration in Concrete with Various Severity Levels

The primary purposes of this study are to investigate the feasibility of electrochemical deposition treatment (EDT) as a comprehensive rehabilitation method for corrosion-induced deterioration in reinforced concrete with various severity levels, and to propose a guideline for the determination of critical factors to advance EDT. This study includes three experimental phases, each of which simulates the initiation (de-passivation), propagation (high corrosion activity), and acceleration (formation of a surface-breaking crack) periods of corrosion-induced deterioration. After completion of a series of accelerated corrosion tests, damaged concrete samples with different severity levels are rehabilitated by a series of EDT processes using a MgCl2 solution in an electrolyte. The main variables for this experiment are the concentration levels (0, 0.3, 1.0 and 3.0 M) of a MgCl2 solution for test phase 1, charging time (0, 2, and 7 days) in EDT for test phase 2, and configuration of pre- and post-treatment processes in EDT for test phase 3. The rehabilitation performance of EDT is evaluated by analyzing the AC impedance properties of the steel-and-concrete interface using electrochemical impedance spectroscopy (EIS) for the test phases 1 and 2, and microscopic alternation in concrete cracks using optical microscopic image and SEM/EDX. It is demonstrated that EDT is an effective method for preventing and mitigating corrosion-induced deterioration in the initiation and rust propagation periods of corrosion and for repairing (closing and filling) a corrosion-induced surface-breaking crack in the acceleration phase of corrosion. Corrosion-resistant performance of concrete increases as the concentration levels of a MgCl2 solution in an electrolyte increases and as the charging time in EDT increases. In addition, a post-treatment process (applying a NaOH solution) after the electrochemical deposition process significantly improves crack-repairing performance of EDT.

Magnesium Salt Influenced Strength Behavior of Lime-Fly Ash Stabilized Fine Grained Soil

The fine grained soil subgrade in coastal areas has the characteristics of high underground water level and serious salinization, and the lime-fly ash stabilized soil (LFSS) often used as the road base material. In order to study the effect of magnesium salt on the material strength, 5 % MgCl2 solution was used to simulate the groundwater magnesium salt environment, and specimens with 7 d, 14 d, 28 d, 60 d and 90 d curing ages were tested in MgCl2 solution for 1 d, 5 d, 10 d, 15 d or 30 d. A controlled test was also conducted in purified water. Strength mechanism of LFSS was analyzed; SEM test was taken; and the influence mechanism of MgCl2 medium was analyzed. The results showed that MgCl2 medium, immersing time, and curing age have effects on compressive strength of LFSS. More specifically, although the early strength is low, the strength of LFSS maintains slow and steady growth from 7 d to 90 d. Long-term immersing in both MgCl2 solution and purified water will reduce the strength of LFSS, while the strength of specimen immersed in MgCl2 solution will decrease faster. Reactions between MgCl2 and LFSS destroyed the original gels and crystals, causing a negative impact on the strength of LFSS. However, with the test dose of MgCl2, the reduced strength of LFSS can still satisfy the sub-base requirement of second-class highway in China.

Phosphorus recovery from urine by adding difference sources of magnesium ion, applying for rural, coastal and island areas in Vietnam

In coastal areas and islands, farmlands often lack of nutrients. This research assessed the precipitation of phosphorus presenting in urine in the form of struvite of magnesium ammonium phosphate (MAP) by adding of supplement of Mg2+ ion from MgCl2 solution contained in seawater (Cat Ba island area). The urine and seawater have been mixed at different ratios. The results have shown [Mg]:[PO4] ratios ranging from 0.75 to 5.26 allowed the precipitation of more than 90% of the phosphorus in the urine. Seawater – to – urine ratios of 0.67/1, 1.3/1, 3.2/1, 5/1, 7/1 and 9/1 in volume would give phosphorus recovery efficiency of 99%, 92%, 96%, 96%, 95% and 99%, respectively. Seawater in the studied area could be an appropriate Mg2+ ion source to produce MAP from urine diverting dry toilets. Recovered phosphorus can be used as slow releasing fertilize for farming. Keywords: MAP: phosphorus recovery; seawater; urine; struvite. Received 24 October 2018, Revised 23 December 2018, Accepted 29 January 2019