Effect of phosphate on the crystallization of hematite, goethite, and lepidocrocite from ferrihydrite
Effect of phosphate on the crystallization of hematite, goethite, and lepidocrocite from ferrihydrite
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DOI：
10.1346/ccmn.1999.0470306
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发表时间：
1999-06-01
影响因子：
2.2
通讯作者：
Torrent, J
中科院分区：
文献类型：
--
作者：
Gálvez, N;Barrón, V;Torrent, J
研究了含磷酸盐的Fe（NO3）（3）溶液水解制备的水铁矿的结晶过程。在不同pH（3-9）下研究了结晶。温度（298，323和373 K），和初始P/Fe原子比为730 d。一般而言，当P/Fe > 2.5%时，结晶受到抑制或仅形成结晶不良的纤铁矿。磷酸盐有利于形成的赤铁矿针铁矿在所有温度下的pH值和P/Fe的范围内调查。这一结果是一致的模型，其中磷酸盐作为模板的赤铁矿形成，类似于其他阴离子，如草酸盐。然而，针铁矿在碱性pH和P/Fe > 1%时优先形成，这可能是因为高磷酸盐浓度导致水铁矿颗粒的负电荷大幅增加。这反过来又导致较少的聚集，这是一个已知的过程之前脱水赤铁矿。磷酸盐对赤铁矿和针铁矿的形貌有很大影响。赤铁矿常呈椭圆形或纺锤形。当P/Fe > 1%时，在碱性条件下形成以赤铁矿为核心的针铁矿孪晶。赤铁矿和针铁矿颗粒都以吸留的形式掺入磷酸盐，不能通过反复碱处理解吸。
We investigated the crystallization of ferrihydrite prepared by hydrolysis of Fe(NO3)(3) solutions containing phosphate. Crystallization was studied at different pH (3-9). temperatures (298, 323, and 373 K), and initial P/Fe atomic ratios for periods to 730 d. Generally, crystallization was inhibited or only poorly crystallized lepidocrocite was formed at P/Fe > 2.5%. Phosphate favored the formation of hematite over goethite at all temperatures for most of the pH and P/Fe ranges investigated This result is consistent with a model in which phosphate acts as a template for hematite formation, in analogy with other anions, such as oxalate. However, goethite was preferentially formed at alkaline pH and P/Fe > 1%, probably because high phosphate concentration resulted in a large increase in the negative charge of the ferrihydrite particles. This resulted in turn in less aggregation, a process that is known to precede dehydration to hematite. Phosphate greatly influenced the morphology of hematite and goethite. Hematite was often ellipsoidal or spindle-shaped. Twinned goethite crystals with a hematite core were formed at alkaline pH at P/Fe > 1%. Both hematite and goethite particles incorporated phosphate in an occluded form not desorbable by repeated alkali treatments.