The inhibiting effectiveness of silicate- and phosphate-based surface-coating agents (Na 2 SiO 3 and KH 2 PO 4 ) to the oxidation of iron sulfide minerals was investigated using pyrite and rock samples containing iron sulfide minerals. The film formed with both surface-coating agents was identified by surface analysis. The oxidation of pyrite surface, layered with iron-silicate or -phosphate, was inhibited (77 and 23%, respectively) under accelerated oxidizing conditions with H 2 O 2 , as measured based on the SO 4 2− concentration in the leachate. Oxidation of coated rock samples with iron-silicate or -phosphate was reduced by up to 54 and 33%, respectively. The inhibitory effects under rainy and submerged conditions were investigated using column experiments. Submerged conditions accelerated deterioration compared to that under rainy conditions. KH 2 PO 4 had a significantly better oxidation-inhibitory effect than Na 2 SiO 3 , and at a concentration of 0.3 M, H + elution was inhibited by more than 90% throughout the experiment. Methods for effective film formation was investigated in terms of producing Fe 3+ ; (1) application of coating agents mixed with oxidant (H 2 O 2 ), (2) application of coating agent after the use of the oxidant. The use of a surface-coating agent after applying an oxidant did not inhibit oxidation. The surface coating agent and the oxidizing agent should be applied as a mixture to form a film.

As treatment of Mn using alkaline agents requires pH of >9 and oxidants such as potassium permanganate is expensive, novel technologies utilizing passive slag reactor is needed. In this study, Mn and Ni of mine drainage were treated in column- and pilot-scale slag reactors for ~1 yr. The outflow of column was mainly saturated with manganite and sometimes with rhodochrosite. A lot of birnessite which has a low point of zero charge and sorbed Ni was observed in the generated precipitates of the reactor using a scanning electron microscopy-energy dispersive spectroscopy. This suggests that adsorptive removal of Ni was effective although most of outflow samples were undersaturated with Ni precipitates. In the pilot-scale experiments, the increase of pH by steel slag resulted in supersaturation of manganite and rhodochrosite as the inflow had relatively high alkalinity of 139–252 mg/L as CaCO 3 . Mn concentrations at the outflow of the pilot-scale slag reactors decreased with time when assessed at similar pOH ranges. This result could be attributed to the autocatalytic oxidation by MnO 2 which accumulated in the pilot-scale reactors. Thus, the utilization of the slag reactor with accumulating Mn oxides can be a promising technology to remove Mn and Ni.

Mixed substrate of steel slag and limestone were applied in reactors to evaluate resistibility to Fe. Steel slag mixed with limestone could decrease Mn from 32–46 mg L-1 to <3 mg L-1 with addition of 4.5–24.4 mg L-1 of Fe in the bench-scale experiment. In the pilot-scale experiments in five mines in South Korea, 95–99% of Mn was removed during the maximum test period of 4 years. Precipitation as Fe and Mn carbonates may have contributed to the Mn removal and resistibility to Fe.

This work newly employed monoclinic zirconia (ZrO2) as a promoter to improve CO2 pyrolysis of coffee waste (CW). The CO2 pyrolysis of CW presented the high level of CO production (14.3 mol%) during two stages of non-isothermal (280 to 700 degrees C) and isothermal pyrolysis (kept at 700 degrees C). At the same condition, the incorporation of ZrO2 improved the CO generation up to about twice that of CW (29.5 mol%) by possibly inducing more conversion of pyrolytic oil into gas. The characterization results exhibited that ZrO2-impregnated biochar (ZrB) possessed the distinctive surface morphology that highly graphitic- and porous carbon layers were covered by ZrO2 nanoparticle clusters. In a series of adsorption experiments, ZrB composite showed pH-dependent As(V) adsorption and pH neutralization ability. The adsorption proceeded relatively rapid with 95% removal during 120 min in the early stage, followed by 5% removal in the remaining 240 min. The maximum adsorption capacity was found to be 25.2 mg g(-1) at final pH 8. The reusability and stability of ZrB were demonstrated in the 6 consecutive cycles of adsorption/desorption. As a result, ZrO2-assisted CO2 pyrolysis can potentially produce fuel gas with high CO fraction and composite adsorbent suitable for As(V) removal in acidic wastewater.

In this work, we newly synthesized granular composite (GASA) via hydrothermal treatment of polyaluminum chloride (PAC) and subsequently granulation pelleting with starch gel as an organic binder. The resulting composite was characterized with analytic instruments, and the feasibility of utilizing GASA as adsorbent for the removal of fluoride (F-) was tested in the batch and column experiments. The characterization results revealed that GASA possessed a spherical/porous framework consisting of aluminosilicate (i.e., ordered albite, NaAlSiO3O8). The results of final pH effect experiments and XRD/XPS analyses showed the dominant adsorption mechanisms of F- on GASA were electrostatic attraction by protonated surface Al-OH, ligand exchange between surface hydroxyl groups and F ions, and surface precipitation (i.e., cryolite formation). Based on the results of adsorption kinetics and adsorption isotherm, granulation resulted in the relatively slow kinetics of F adsorption compared to the powder type, but was preferred to retain good adsorption capacity. The regeneration possibility of GASA was also proven with the adsorption/desorption cyclic test. In the column study, 15-cm length of the GASA layer and the flow rate less than 0.85 mL min(-1) were proposed to keep the satisfactory level of F in water. The experimental results offer a potential of PAC sludge-derived composite as adsorbent for the removal of F from water. (C) 2020 Elsevier Ltd. All rights reserved.

Among the variables affecting the volume and composition sludge generated in the semi-active mine drainage treatment facility operating in Korea, the effect of CO2 dissolved in the mine drainage on the sludge composition was studied. The water quality change was analyzed by neutralizing 1m3 of mine drainage from the Ilkwang abandoned mine. The neutralization with lime slurry resulted in removal of Fe, Al, Cu and SiO2, and an increase in Ca content in neutralized water. The dissolved CO2 in raw water was 56 mg/L but decreased to <1 mg/L after neutralization. The dissolved CO2 in the mine drainage can be consumed to form calcite or be removed by degassing before neutralization. There is also a possibility that gypsum may be produced depending on pH due to the high concentration of Ca and SO4 enriched. The amount of sludge generated through the neutralization test was insufficient for analysis. Therefore, chemical analysis and mineral assessment were performed on the effluent, sludge and cakes generated in the settling pond in the Ilkwang abandoned mine. XRD analysis showed that calcite (CaCO3) and Bassanite (CaSO4 · H2O) were commonly found in red and white sludge. CO2 in the mine drainage reacted with CaO to affect the sludge composition. As a result of the XRF, white sludge contained 35.57% of CaO, indicating that a large amount of slaked lime was included. Red sludge and cakes had a Fe2O3 content of more than 35%, so iron was the main ingredient. In addition, the CaO content was analyzed as 15.28%, the second major component. As a result of measuring the paste pH of the dehydrated cake, it can be seen that the pH is in the range of 9 to 10 due to CaO. The sludge shows strong alkali characteristics, indicating that slaked lime remains in the sludge. The remaining slaked lime will increase the sludge volume and increase the sludge management costs.

Aqueous arsenate [As(V)] was removed using an aluminum-based adsorbent (ABA) and coal mine drainage sludge coated polyurethane (CMDS-PU) prepared using alum and coal mine sludge, respectively. Their As(V) removal efficiencies were compared with each other and granular ferric hydroxide (GFH). The mineralogy and surface chemistry of materials were determined using wavelength dispersive X-ray fluorescence (WD XRF) and Fourier transform infrared spectroscopy (FFIR), respectively. The angle-resolved X-ray photoelectron spectroscopy (AR-XPS) studies confirmed As(V) retention on the adsorbent surfaces. The adsorption kinetics data were fitted to pseudo second-order rate equation. The faster As(V) uptake kinetics of GFH and ABA (GFH > ABA > CMDS-PU) were attributed to their large pore volume and mesoporous nature. Langmuir adsorption capacities of 22, 31 and 10 mg/g, were achieved for GFH, ABA and CMDS-PU, respectively. As(V) adsorption on GFH, ABA and CMDS-PU was endothermic. GFH and ABA were efficient over a wide pH range (3-10). In column studies, GFH, ABA, and CMDS-PU successfully treated 23625, 842, and 158 bed volumes (BVs) and 2094, 6400, and 17 BVs of As(V)-contaminated water with 9.5 and 27 EBCT, respectively (at pH = 6.0, As-i = 600 mu g/L). The GFH and ABA have a potential to be used at large-scale aqueous phase As(V) remediation. (C) 2019 Elsevier Ltd. All rights reserved.

In this study, the effect of neutralizer type and concentration, target pH, and elapsed time on sludge volume were evaluated using Ilkwang mine drainage. A higher neutralizer concentration produced more sludge when the pH 7 was neutralized with 5%, 10%, and 20% lime slurry. Neutralization with the same pH with 20% lime and NaOH resulted in less sludge when using lime. The type of neutralizer affected the amount of sludge produced. However, regardless of the type of neutralizer, the volume of the sludge rapidly shrank within one hour and slowly declined thereafter. The control of pH 7 and 10 with 20% lime resulted in considerable sludge at a high pH. A comparison of sludge with 1 L and 1 m3 neutralized mine drainage showed 9% and 10% sludge volume, respectively, as compared to raw mine water. A beaker neutralization experiment was also able to estimate reliable sludge generation.