The Inhibition of Fluoride Elution from Industrial Wastes with Portland Cement, Calcium and Magnesium Salts in Alkaline Region

Xiaoxu Kuang, A. Sasaki, M. Endo
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引用次数: 1

Abstract

Recycling of fluoride industrial wastes is difficult to dispose, since the fluoride ions eluted again easily. In this study, newly effective inhibition method in both neutral and alkaline region for fluoride elution was investigated. Fluoride elution concentration from CaF2 was 9.8 mg/L at pH 8.1 and 288.5 mg/L at pH 12.2 with water/solid ratio of 10. Additions of Ca(OH)2, CaCl2 and NH4H2PO4 could restrain fluoride elution concentration of CaF2 to 0.22 mg/L in the neutral region. This inhibition of fluoride elution was due to a generation of hydroxyapatite (HAp) or chlorapatite (ClAp) which has high ion exchange capacity. Additions of Portland cement, Ca(OH)2 and MgCl2 could restrain fluoride elution concentration of CaF2 to 0.47 mg/L in alkaline region. It was only 0.16% of 288.5mg/L which was the fluoride elution concentration from CaF2 at pH 12.2. The elution of fluoride ions was restrained by the coprecipitating of CaF2 with the high content of Ca 2+ provided from Ca(OH)2 and cement hydrates. The carbonation of Ca 2+ was prevented by the addition of Mg. Moreover, the forming of ettringite with a high ion-exchange capacity and the solidification effect of Ca-bearing hydrates contributed to the inhibition of the elution of fluoride. These additives for the practical industrial wastes, such as paper sludge and coal ash, with high concentration of fluoride were conducted. The result indicates that the fluoride elution could be restrained to meet the environmental standard (0.8 mg/L) in Japan in alkaline region. This inhibition method for fluoride elution would be able to contribute to promotion of recycling of fluoride industrial wastes.
硅酸盐水泥、钙镁盐对碱性地区工业废水中氟的抑制作用
含氟工业废物的回收处理较为困难,因为其中的氟化物离子很容易被再次洗脱。在本研究中,研究了在中性和碱性区域对氟洗脱的新的有效抑制方法。在pH 8.1和pH 12.2条件下,CaF2对氟的洗脱浓度分别为9.8 mg/L和288.5 mg/L,水固比为10。Ca(OH)2、CaCl2和NH4H2PO4的加入可将CaF2的氟洗脱浓度抑制在中性区0.22 mg/L。这种抑制氟洗脱的作用是由于产生了具有高离子交换能力的羟基磷灰石(HAp)或氯磷灰石(ClAp)。在碱性区,硅酸盐水泥、Ca(OH)2和MgCl2的加入可抑制CaF2的氟洗脱浓度为0.47 mg/L。仅为pH为12.2时CaF2对氟的洗脱浓度288.5mg/L的0.16%。Ca(OH)2和水泥水合物提供的大量ca2 +与CaF2的共沉淀抑制了氟离子的洗脱。镁的加入阻止了ca2 +的碳酸化。此外,高离子交换容量钙矾石的形成和含钙水合物的凝固作用对氟的洗脱有抑制作用。对造纸污泥、粉煤灰等含高浓度氟化物的实际工业废渣进行了试验研究。结果表明,在碱性地区可抑制氟的洗脱,达到日本环境标准(0.8 mg/L)。这种抑制氟洗脱的方法将有助于促进含氟工业废物的回收利用。
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