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Dissolution rates of amorphous Al- and Fe-phosphates and their relevance to phosphate mobility on Mars.

机译：无定形铝和铁磷酸盐的溶解速率及其与火星上磷酸盐迁移率的关系。

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摘要

Phosphate is an essential element for life on Earth, and therefore if life exists or ever existed on Mars it may have required phosphate. Amorphous Al- and Fe-phosphates rapidly precipitate from acidic solutions and amorphous Al-phosphates likely control phosphate concentrations in some natural waters on Earth. Amorphous phases may be even more important on Mars than on Earth, and amorphous phosphates are therefore likely important in the phosphate cycle on Mars. Despite this importance, however, few dissolution rates exist for amorphous Al- and Fe- phosphates. In this study, dissolution rates of amorphous Al- and Fe-phosphates were measured in flow-through reactors from steady state concentrations of Al, Fe and P. A pH--dependent rate law was calculated from the dissolution rates log R = log k -- npH, where R is the dissolution rate, k is intrinsic rate constant and n is the rate dependence on pH. For amorphous Al-phosphate, log k = -6.539 +/- 1.529, and n = 2.391 +/- 0.493. For amorphous Fe-phosphate, log k = -13.031 +/- 0.558, and n = 1.376 +/- 0.221. Amorphous Al-phosphate dissolves stoichiometrically under all conditions, and amorphous Fe-phosphate dissolves non-stoichiometrically, approaching stoichiometric dissolution as pH decreases, due potentially to Fe-oxides precipitating and armoring grain surfaces. Perhaps due to these effects, amorphous Al-phosphate dissolution rates are approximately three orders of magnitude faster than amorphous Fe-phosphate dissolution rates. Amorphous Al-phosphate dissolution rates measured in this study are also faster than published variscite dissolution rates. Dissolution rates of amorphous Al- and Fe-phosphates in this study therefore imply rapid phosphate release into acidic environments, suggesting phosphate mobility under Mars-relevant conditions.
机译：磷酸盐是地球生命的重要元素，因此，如果生命存在或曾经存在于火星上，则可能需要磷酸盐。无定形的铝和铁磷酸盐迅速从酸性溶液中沉淀出来，无定形的铝磷酸盐可能控制了地球上某些自然水中的磷酸盐浓度。非晶相在火星上的重要性甚至比在地球上更为重要，因此无定形磷酸盐可能在火星的磷酸盐循环中很重要。尽管具有这种重要性，但无定形的磷酸铝和磷酸铁的溶解速率却很少。在这项研究中，通过稳定浓度的Al，Fe和P测量流通式反应器中无定形的Al和Fe磷酸盐的溶解速率.pH依赖的速率定律由溶解速率log R = log k计算得出-npH，其中R是溶解速率，k是固有速率常数，n是速率对pH的依赖性。对于无定形磷酸铝，log k = -6.539 +/- 1.529，n = 2.391 +/- 0.493。对于无定形磷酸铁，log k = -13.031 +/- 0.558，n = 1.376 +/- 0.221。无定形磷酸铝在所有条件下均以化学计量方式溶解，而无定形磷酸铁则以化学计量方式溶解，随着pH降低，接近化学计量溶解，这可能是由于铁氧化物沉淀和铠装了晶粒表面所致。也许由于这些作用，非晶态磷酸铝的溶解速率比非晶态磷酸铁的溶解速率快大约三个数量级。在这项研究中测得的无定形磷酸铝溶解速率也快于已发表的无水碳酸钙溶解速率。因此，本研究中无定形铝磷酸盐和铁磷酸盐的溶解速率意味着磷酸盐快速释放到酸性环境中，这表明在与火星有关的条件下磷酸盐的迁移率。

著录项

  • 作者

    Tu, Valerie M.;

  • 作者单位

    University of Nevada, Las Vegas.;

  • 授予单位 University of Nevada, Las Vegas.;
  • 学科 Planetology.;Geology.;Geochemistry.
  • 学位 M.S.
  • 年度 2013
  • 页码 36 p.
  • 总页数 36
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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