報告書番号

U02046

タイトル（和文）

モリブデンの土壌への吸着と土壌有機物への取込み

タイトル（英文）

Molybdenum Adsorption on various Soils and Incorporation into Soil Organic Matter

概要 （図表や脚注は「報告書全文」に掲載しております）

石炭灰中の微量元素のうち、環境基準上の規制項目化が予想されるモリブデンを対象に選び、国内の代表的土壌を対象にモリブデンの吸着特性と溶液中からの除去に及ぼす土壌有機物の影響を検討し以下の結論を得た。(1)吸着特性：モリブデンが土壌に吸着するときの溶液ｐHは2～7の酸性・中性の範囲であり、溶液pHが8～12のアルカリ性領域では土壌に吸着しない。この原因は溶液ｐHと酸化還元電位で規定されるモリブデンの化学形態と土壌の荷電状態の関係により説明できる。(2)土壌有機物への取込み：石炭灰溶出水を模擬したアルカリ性溶液と土壌との接触によって土壌有機物が溶解し、溶液のｐHが低下するとともに有機物が凝集し始め、最終的には有機物沈澱にモリブデンが取り込まれる。(3)取込み量の評価：モリブデンの土壌への吸着量はホウ素とほぼ同程度できわめて小さく、他の微量元素の分配係数と比較しても、土壌に吸着しにくい元素である。

概要 （英文）

Molybdenum(Mo) is one of the monitored substances and recognized nutrient elements considered to be essential for the growth of plants and caused molybdenum(Mo)-induced copper(Cu) deficiency in ruminant animals. Furthermore, it is suggested that various kinds of coal fly ash from electric fire power plants contain small amounts of Mo as trace elments, most of solutions in contact with coal fly ash exhibit high pH, and the pH of the eluent is gradually lowering with permeate into soil layers. However, the effects of lowering pH in alkaline water on adsorption characteristics of Mo have not been sufficiently investigated. Consequently, it is important to assess several effects of soil matrix on migration process through soil layers and adsorption characteristics of Mo onto various soils. 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 the aerobic condition and room temparature(22±3℃). The adsorption characteristcs of Mo on various soils were investigated as a function of solution pH, Mo concentration, ionic strength, competing anion concentrations 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 is capable of adsorbed on various soils exhibits about pH 2 to 7,on the contrary, it dose not sufficiently exhibit at high pH extending about pH 8 to 12, because the magnitude of Mo adsorbed on various soils is dependent on the soil solution pH, the existence of Mo species in solution and the electric charge of soil particle surface. (2)Incorporation of Mo into soil organic matter : The organic matter, amorphous hydroxide of aluminum(Al) and iron(Fe) are diluted from soil matrix when allowed to stand in contact with alkaline solution. Dissolved organic matter precipitates as a dark brown crystalline solid with acidification of dilution and most of the dissolved Mo are ultimately incorporated into the organic precipitation. (3)Evaluation by incorporated Mo : The magnitude of Mo adsorbed on various soils is approximately the same as that of Boron(B) and Mo is not liable to adsorb on the suface of soil particle by comparison with distribution coefficients of other trace elements such as Arsenic(As) and Chromium(Cr).

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