Joo Sung Ahn

Arsenic removal using steel manufacturing byproducts as permeable reactive materials in mine tailing containment systems

Steel manufacturing byproducts were tested as a means of treating mine tailing leachate with a high As concentration. Byproduct materials can be placed in situ as permeable reactive barriers to control the subsurface release of leachate from tailing containment systems. The tested materials had various compositions of elemental Fe, Fe oxides, Ca-Fe oxides and Ca hydroxides typical of different steel manufacturing processes. Among these materials, evaporation cooler dust (ECD), oxygen gas sludge (OGS), basic oxygen furnace slag (BOFS) and to a lesser degree, electrostatic precipitator dust (EPD) effectively removed both As(V) and As(III) during batch experiments. ECD, OGS and BOFS reduced As concentrations to <0.5mg/l from 25mg/l As(V) or As(III) solution in 72 h, exhibiting higher removal capacities than zero-valent iron. High Ca concentrations and alkaline conditions (pH ca. 12) provided by the dissolution of Ca hydroxides may promote the formation of stable, sparingly soluble Ca-As compounds. When initial pH conditions were adjusted to 4, As reduction was enhanced, probably by adsorption onto iron oxides. The elution rate of retained As from OGS and ECD decreased with treatment time, and increasing the residence time in a permeable barrier strategy would be beneficial for the immobilization of As. When applied to real tailing leachate, ECD was found to be the most efficient barrier material to increase pH and to remove As and dissolved metals.

Removal capacity of water plant alum sludge for phosphorus in aqueous solutions

Abstract Alum sludge, which is a waste product from a potable water treatment process, was tested as an inexpensive alternate adsorbent for phosphorus in wastewater. The sludge was composed dominantly of sand size aggregates, and could remain stable in aqueous media. The majority of reactive Al in alum sludge was present as an amorphous phase, and seemed to be the major absorbent for P. The batch sorption test showed that the removal of P was influenced by the solubility of Al, Fe and organic carbon depending on pH condition. The acidic condition favored the removal of P, and there was a side effect in the P removal process such as dissolution of Al and organic C at acidic (pH < 4) and alkaline (pH < 8) conditions. The pH range from 4 to 6 was effective for all inorganic and organic phosphates with a low solubility of Al and organic C. The maximum adsorption capacity of alum sludge was calculated as 25,000 mg/kg for orthophosphate, and followed the order: orthophosphate > pyrophosphate > triphosphate > organic phosphate (adenosin). From the column test with a 30 mg/L orthophosphate solution at a flow rate of 3.0 ml/min, the alum sludge removed P to less than 1.0 mg/L over 250 pore volumes at initial pH 4, and 200 pore volumes at initial pH 5, respectively.

Arsenic contamination of soils and sediments from tailings in the vicinity of Myungbong Au mine, Korea

Abstract Geochemical characteristics of As contamination in the Myungbong gold mine area in Korea were investigated, and the mine tailings were found to contain high concentrations of As (2,500–6,420 mg/kg). The mine tailings are an obvious candidate for the source of contamination in the study area. From the sequential, and oxalate, extraction analyses the majority of the As in the tailings was found to be associated with Fe oxides produced when sulfide minerals are oxidised. Mineralogical examinations showed the formation of poorly crystalline Fe oxides on a rim of pyrite, onto which the As was retained. The sediments of two ponds affected by the tailings also contained significant levels of As. High concentrations of dissolved As were also found in pond and stream waters. It has been suggested that the mobility of the As was increased by the reductive dissolution of Fe oxides under reducing conditions in the pond. Agricultural fields, located beneath the tailing dumps, have been contaminated by the continuous use of contaminated stream water and groundwater for irrigation.

Comparison of arsenic co-precipitation and adsorption by iron minerals and the mechanism of arsenic natural attenuation in a mine stream

Mine stream precipitate collected from Ilkwang mine, Korea, contained high concentrations of arsenic (As), while water collected from the same site had negligible As concentrations, indicating natural attenuation of As occurred in the mine stream. The mechanism of attenuation was explained by comparison of X-ray absorption near edge structure (XANES) of As(V) co-precipitated with or adsorbed to iron (Fe) minerals in mine precipitates. Arsenic in the mine precipitate was present as As(V) and schwertmannite was the main Fe mineral. Arsenic co-precipitation with schwertmannite was the major mechanism of As removal in the mine stream, followed by As adsorption by goethite and As co-precipitation with ferrihydrite. Schwertmannite and ferrihydrite were formed in acid mine drainage and As was incorporated in their structure during formation. Additionally, schwertmannite and ferrihydrite may transform to goethite with As adsorbed onto the goethite surface. Based on the results of batch experiments of As co-precipitation and adsorption, co-precipitation of As with ferrihydrite and schwertmannite was the most effective As sequestration mechanism in the removal of As(V) from acid mine drainage.

An engineered cover system for mine tailings using a hardpan layer: A solidification/stabilization method for layer and field performance evaluation

A cover system for mine tailings with a solidified layer (called an engineered hardpan) was developed in this study to reduce water infiltration, acid generation and sulfide oxidation. Hydrated lime and waterglass were used to produce calcium silicate, which can serve as a binder when constructing a hardpan layer. The compressive strength of each solidified/stabilized material was found to be sufficient in the lab, and the amounts of heavy metals were significantly reduced in chemical leaching tests. Various characteristics of tailings may affect the layers mechanical strength early on, but a long curing period is capable of compensating for these effects. Heavy metals were stabilized as carbonate-bound phases and sulfide minerals were surrounded by calcium silicate matrix, thereby preventing further reaction. To evaluate the field performance of the system, a hardpan layer was installed on top of tailings on a pilot scale. Leachate with high salt content was generated in the tailings layer in the early stages of monitoring, but after approximately 6 months, the objective was achieved as the hardpan layer gradually stabilized. Notably, during the heavy rainfall season of the later monitoring stage, water infiltration was continuously prevented by the system.

Environmental Contamination and Sequential Extraction of Trace Elements from Mine Wastes Around Various Metalliferous Mines in Korea

ABSTRACT This study has focused on the environmental problems of toxic trace elements from mine wastes including tailings around various abandoned metalliferous mines in Korea. 48 mine wastes were sampled in and around 38 abandoned mines classified as 3 groups (Au-Ag, base metal and other mines) with 5 types by their ore minerals and mineralization. Wide ranges of pH values were found in the wastes derived from the weathering process of parent rocks; relatively low pH due to the oxidation of sulfide minerals (mainly pyrite) and high pH related to the interaction with carbonate minerals (mainly calcite) or to absence of sulfide minerals. Based on the 0.1N HCl extraction analysis, elevated levels of Cd, Cu, Pb and Zn were found in a few mine wastes, especially for type 2 (Au-Ag mine mineralized by a hydrothermal vein type with sulfide minerals), and some wastes from types 4 (skarn type) and 5 (others) contained over the guidelines (action level) of Cd and/or Cu under the Soil Environment Preservation Act in Korea. In addition, extremely high concentrations of the metals were also found in the mine wastes extracted by aqua regia compared to soils from uncontaminated natural areas. This was also confirmed by the results of sequential extractions performed on representative samples, which showed high proportions of the metals in exchangeable fractions of the acidic mine wastes. Thus, it can be expected that trace elements in the mine wastes may be dispersed both downstream and downs-lope through water and wind. Eventually they may pose a potential health risk to residents in the vicinity of the mine. Therefore, it is necessary to control the mine wastes with a proper method for their reclamation such as neutralization of the mine wastes using pulverized limestone.

Laboratory Investigation of the Geochemical Behavior of Metals in Paddy Soils Contaminated with Mine Tailings

The geochemical behavior of metals, including Fe, Mn, Pb and Zn, in contaminated paddy soils was investigated during the cultivation of rice crops through laboratory microcosm experiments. From the two paddy fields contaminated by mine tailings, Siheung and Deokeum in Korea, paddy soils were collected and analyzed for their geochemical characteristics. The Siheung paddy soil showed higher levels of heavy metals, whereas the higher potential for the release of metals was anticipated due to the extremely acidic conditions at Deokeum. In microcosm experiments of flooded paddy soils over 18 weeks, Fe and Mn were released in subsurface pore waters by reductive dissolution, and Pb and Zn were dissolved in high amounts at the surface by oxidation of sulfides. Although amorphous Fe oxide-rich layers were formed at the surface of both paddy soils, the release of Pb and Zn were controlled at the surface by these layers only under slightly alkaline conditions at Siheung. Lead and Zn were associated with the reducible and carbonate fractions at the surface paddy soil of Siheung from the sequential extraction on core samples collected during the flooded period. In the acidic conditions at Deokeum, Pb and Zn were continuously released until the late stage of flooding. A great increase in the exchangeable fraction of metals was observed after the soils had drained. The bioavailability of metals for rice crops would be high under acidic conditions at Deokeum, despite the lower levels of heavy metal contamination.

Geochemical Distributions of Heavy Metals and Cr Behavior in Natural and Cultivated Soils of Volcanic Jeju Island, Korea

ABSTRACT Volcanic ash soils, representative soil series (Andisols) on Jeju Island, Korea were collected to investigate the geochemical and mineralogical characteristics. Distributions of heavy metals and Cr behavior, in particular, were further assessed according to land uses (natural or cultivated). The natural soil samples had ferromagnesian minerals mostly in mineralogy, high levels of organic matter, silty textures, and acidic pH. Low amounts of SiO2 and high contents of Al2O3 and Fe2O3, were found in the Jeju soils, which are typical characteristics of Andisols compared to other soil orders. The mean total concentrations of Zn (127 mg/kg), Ni (183 mg/kg), Co (84 mg/kg), and Cr (677 mg/kg) were higher than worldwide values in most of the natural soils. Especially, Cr was a main soil contaminant, exceeding 1000 mg/kg in some soil series. The relationships between heavy metals and major elements indicated a ferromagnesian mineral origin for heavy metals and secondary associations with Fe and Al oxides during weathering processes. Cultivated soils also had similar volcanic ash soil properties, but showed more clayey textures, greater SiO2, and lower Al2O3 and Fe2O3 contents compared to natural soils. The average heavy metal content was not affected by cultivation, and characteristic behavior was maintained, except for slight increases in Cu, Pb, and Zn contents in surface soils because of fertilizer inputs. The only distinct decrease was in Cr content in the surface and subsurface of cultivated soils. This decrease might reflect the formation of a soluble organic complex of Cr(III), based on the significant increase in the sodium pyrophosphate-extracted fraction in sequential extractions. However, the high reducing capacities of volcanic ash soils compared to inland non-volcanic soils suggest that the potential for contamination by Cr(VI) can be significantly very low.

Assessment of the potential occurrence of acid rock drainage through a geochemical stream sediment survey

During large constructions of roads or structures, unexpected acid rock drainage (ARD) can be caused by local mineralization containing sulfides in the geology. The potential of ARD occurrence of a certain area sometimes must be assessed before initiation of any engineering earth works. However, it is difficult to assess the entire area through collecting rock samples and predicting the potential by laboratory tests, such as the acid–base accounting method. In this study, a new prediction protocol using a geochemical exploration survey technique of stream sediment is proposed. Sediment samples were collected at the case study area where a large development is expected in the future, and the contents of some major and heavy metal elements were compared according to the major geologies of the sampling points. The modified geoaccumulation indices (Igeo) of Fe, Pb and As could indicate a possible zone of pyrophyllite mineralization, which may cause the occurrence of ARD at the study area. Using the enrichment index of the three elements relative to the median values of the area, a high potential zone of ARD could be designated, which was in agreement with the laboratory ARD prediction tests of the rock samples. In the other areas with different mineralization processes, other metallic elements can be selected as indicators of the ARD potential. Likewise, the potential of the occurrence of ARD at an area can be assessed by evaluating the geochemical distributions and drawing the indicator elements for ARD through a stream sediment survey.

Interaction of Sb(III) with iron sulfide under anoxic conditions: Similarities and differences compared to As(III) interactions

This study examined the reaction mechanism of arsenite, As(III), and antimonite, Sb(III), with iron sulfide and compared their pH-dependent reaction behaviors under strictly anoxic environments. The comparison of Sb(III) with As(III), based on their chemical similarity, may provide useful insight into understanding the geochemical behavior of the less studied Sb(III). The pH-dependent batch sorption studies revealed that As(III) and Sb(III) displayed similar removal trends with pH in terms of the removal efficiency. However, the aqueous As(III) species transformed to thioarsenite species, while aqueous Sb(III) species remained inert under the highly sulfidic anoxic system. An X-ray absorption spectroscopy study demonstrated the reaction of As(III) and Sb(III) at acidic pH was closely related to the precipitation of sulfide minerals As2S3 and Sb2S3, respectively, as a consequence of the reaction with sulfide produced through mackinawite dissolution. Meanwhile, the removal at basic pH was inferred as a surface reaction, possibly through surface complexation, surface-precipitation, or both. In this study, the pH-dependent Sb(III) uptake mechanisms proved to be similar to the corresponding mechanisms for As(III) uptake, with mackinawite demonstrating a superior capacity to scavenge Sb(III) in ferrous and sulfide-rich reducing environments.