Abstract
Molybdenum (Mo) is one of the monitored substances and recognized nutrient elements considered to be essential for the growth of plants and causes molybdenum (Mo)-induced copper (Cu) deficiency in ruminant animals. Furthermore, it is suggested that various kinds of coal fly ash from coal-fired electric power plants contain small amounts of Mo as trace elements, most solutions in contact with coal fly ash exhibit high pH, and the pH of the eluent is gradually lowering with permeation into soil layers. However, the effects of lowering pH in alkaline water-on adsorption characteristics of Mo have not been sufficiently investigated. The purpose of this study is to clarify the adsorption characteristics of Mo on typical soils in Japan and the effects of soil organic matter on the elimination of Mo from solution. The adsorption experiments were carried out under aerobic conditions and room temperatures of 22±3℃. The adsorption characteristics of Mo on various soils were investigated as a function of solution pH, Mo concentration and soil organic matter using batch experiments. The obtained results are summarized as follows: 1) Adsorption characteristics: The range of solution pH in which Mo was capable of being adsorbed on various soils exhibited about pH 4 to 7; it did not sufficiently exhibit at high pH of 8 to 12, because the magnitude of Mo adsorbed on various soils was dependent on the soil solution pH, the existence of Mo species in solution and the electric charge of the soil particle surface. 2) Incorporation of Mo into soil organic matter: The organic matter was dissolved from soil matrix when allowed to stand in contact with an alkaline solution. Dissolved organic matter precipitated as a dark brown crystalline solid with acidification of dilution and most of the dissolved Mo was ultimately incorporated into the organic precipitation.
