Lead Removal Using Calcium Phosphate Precipitated on the Surface of Phosphorus Adsorbent.

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  • 晶析型リン除去材の表面に析出したリン酸カルシウム結晶による鉛除去
  • ショウセキガタ リン ジョキョザイ ノ ヒョウメン ニ セキシュツ シタ リンサン カルシウム ケッショウ ニ ヨル ナマリ ジョキョ

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Abstract

<p>The removal of lead using calcium phosphate precipitated on the surface of a crystallization type phosphorus adsorbents which were composed mainly of gypsum and calcium carbonate was investigated. Since calcium hydrogen dehydrate(DCPD) precipitated on the surface of phosphorus adsorbent at the time of removing phosphorus did not have ion exchange ability, removal of lead ion was examined after transforming DCPD into hydroxyapatite(HAp) having ion exchange ability with heavy metal ion. The conversion of DCPD to hydroxyapatite was attempted by aging in aqueous solutions of various pHs and temperatures. As a result, it was found that the transformation of DCPD to hydroxyapatite was easy to proceed by aging in an aqueous solution with high temperature and pH. In this study, a phosphorus adsorbent aged in an aqueous solution adjusted to pH 6 with aqueous ammonia at 60 °C was subjected to lead removal experiment because DCPD precipitated on the surface of the phosphorus adsorbent was almost completely transformed into hydroxyapatite under this aging condition. It was revealed that removal of lead ions by a phosphorus adsorbent on which HAp was precipitated on the surface proceeded by ion exchange of HAp and formation of fine crystal particles containing lead. However, the removal ratio of lead ions was about 60 % of the initial concentration of 50 ppm, and about 40 % of lead ions remained in the solution. This result suggested that some of the lead ions formed complexes, such as [Pb(OH)4]2-, with the hydroxide ions eluted from HAp.</p>

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