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 CaF 2 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 , CaCl 2 and NH 4 H 2 PO 4 could restrain fluoride elution concentration of CaF 2 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 MgCl 2 could restrain fluoride elution concentration of CaF 2 to 0.47 mg/L in alkaline region. It was only 0.16% of 288.5mg/L which was the fluoride elution concentration from CaF 2 at pH 12.2. The elution of fluoride ions was restrained by the coprecipitating of CaF 2 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 2+ . 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.
Abstract:The disposal and the reuse of industrial wastes have become increasingly difficult due to the elution of hazardous anions, such as F − , [B(OH) 4 ] − , AsO 4 3− , and CrO 4 2− . Effective methods for removing hazardous ions and reusing solid wastes are urgently required. In this study, Ca(OH) 2 , MgCl 2 , and BaCl 2 were added to reduce the elution concentrations of F, B, As, and Cr by coprecipitating insoluble inorganic salts. After this, ordinary Portland cement (OPC) was added to the ion exchange and solidified with these hazardous ion-containing substances. The addition of crushed stone powder (CSP), which was a by-product of the process of crushing aggregates or sawing stone, inhibited the elution of hazardous ions and improved the inhibition effect of OPC. The elution concentrations of F, B, As, and Cr were successfully reduced from their maximum elution concentration of 10 mg/L to below the environmental standards values of Japan. A simultaneous inhibition method for the elution of F, B, As, and Cr from industrial wastes has been developed successfully and would be able to promote the reuse and recycling of CSP and other industrial wastes.
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