Leaching Behavior Of Trace Elements Research Articles

Leaching behavior of trace elements in coal spoils from Yangquan coal mine, Northern China

The long-term dumping of coal waste piles has caused serious environmental problems. Release of trace elements (including rare earth elements, REEs) from coal spoils gobs was investigated at Yangquan coal mine, Shanxi Province, China. X-ray diffraction (XRD) was used to analyze the mineral composition of the coal spoils. The minerals of the coal-spoil samples are mainly kaolinite and quartz, with a minor proportion of pyrite. The batch and column tests were employed to simulate the leaching behavior of trace elements from coal spoils. Elements V, Cr, Zn, As, Pb, and Cd are highly enriched in all coal spoils. The coal spoils also have elevated levels of Ga, Ge, Se, Sn, Hf, and Th. The leachate of coal spoils, fried coal spoils and CSFGM (coal spoils fire gas mineral) samples are acidic, with the pH values ranging between 3.0 and 6.6. The released elements with high concentrations (over 100 μg/L) include Fe, Mn, Co, Ni and Zn, while moderately-released elements are Cu, Se, Mo and As. A high content of heavy metals in batch-test leachate with CSFGM indicates an increased mobility of heavy metals in coal spoil combustion byproduct. Within the first hour washing with the electrolyte solution, a rapid rise of common cations, trace elements, and REEs content, as well as a drop of pH value, in effluent was observed. An increased leaching velocity favors the release of trace elements from coal spoils. In addition, the pulse input of precipitation led to more elements to be released than continuous leaching.

Leaching Behavior and Potential Environmental Effects of Trace Elements in Coal Gangue of an Open-Cast Coal Mine Area, Inner Mongolia, China

In order to better understand the role of coal gangue in potential environmental and ecological risks, the leaching behavior of trace elements from coal gangue has been investigated in an open-cast coal mine, Inner Mongolia, China. Four comparative column leaching experiments were conducted to investigate the impacts of leaching time, pH values and sample amount on the leaching behavior of trace elements. Enrichment factors (EF), maximum leached amount (Lam), maximum leachability (Lrm), effects range low (ERL) and effects range median (ERM) were employed to evaluate potential environmental and ecological hazards resulting from the leaching behavior of environment-sensitive trace elements from coal gangue. Leaching time and sample amount display important effects on trace element concentrations, leached amounts and leachability. The pH values exhibit a weak influence on the leaching behavior of the selected trace elements (e.g., As, V, Cr, Co, Ni, Cu, Zn, Se, Cd, Sn, Pb and Hg). The coal gangue are enriched in As, Co, Se and Pb and, in particular, show higher environmental pollution levels of As and Se (EF > 2). Lam values suggest that all of the elements investigated do not show potential risk to soils and vegetation, but have a high hazard risk for ground water. Elements including Ni, As, Cr and Zn are inclined to show high or moderate biological toxicity.

EFFECT OF OIL SHALE ASH APPLICATION ON LEACHING BEHAVIOR OF ARABLE SOILS: AN EXPERIMENTAL STUDY

Oil shale ash contains mineral ingredients of agricultural importance and could be used for treatment of soils. However, the ash contains several hazardous ingredients, i.e. toxic trace metals which could be mobile and create environmental concerns. Beneficial use of the oil shale ash in agriculture and forestry requires better knowledge of leaching characteristics of soil-ash systems. In this study two different ash samples have been added to two types of soil, particularly Rendzic Leptosol and Podzolic Gleysols, in order to investigate the leaching characteristics of soil/ash mixtures using the traditional leaching scheme and a scheme modified by pretreatment (incubation) of solid in wet conditions. The pH, conductivity and concentration of Cd, Pb, Cr, Zn and Ni in leachates are determined. The results revealed that transport of hazard components to the water phase was highly dependent on the type of soil and ash and leaching method used. Throughout the experiment, concentrations of heavy metals in leachates of any combination of soil and fly ash are low. The most mobile metals are found to be nickel, zinc and chromium. Application of oil shale ash to soil might increase mobile fraction of Ni in soil. For the safe recycling of oil shale wastes in agriculture, it is recommended to take into account the leaching behavior of trace elements as ingredients in combustion ash.

Quantifying the availability and the stability of trace cationic elements in fly ash

For adsorption–desorption controlled leaching processes, the total leachable mass and the adsorption constant are parameters representing the availability and the stability of trace elements in solid media. With these parameters, one can predict the leaching behavior of trace elements from solids under various pH and solid-to-liquid ratio conditions. An approach was developed in this paper to determine these parameters for model elements Cu(II), Cd(II), and Ni(II) in fly ash. This approach consists of a batch equilibrium titration, a batch equilibrium leaching with and without target element addition, and mathematical modeling. Results indicated that the adsorption constant of a trace element can be determined by modeling the adsorption ratio of the added element to the system as a function of pH. Results also indicated that the trace element originally present in fly ash had similar adsorption–desorption behavior as that added externally. By modeling the batch leaching data with and without external element addition, the total leachable mass and adsorption constant of the target element can be determined simultaneously. The total leachable mass is in agreement with experimental data from 50 mM EDTA extraction.