<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>C. E. Roberson</dc:contributor>
  <dc:contributor>Reba B. Fournier</dc:contributor>
  <dc:creator>J.D. Hem</dc:creator>
  <dc:date>1982</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;Beta MnOOH is precipitated preferentially (with respect to Mn&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;O&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;) at temperatures near O°C when Mn&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;is oxidized in aerated aqueous solutions. Upon aging in solutions open to the atmosphere a slurry of βMnOOH tends to disproportionate to form MnO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and Mn&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;. In such aged solutions, Mn&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and H&lt;/span&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;activities can be constant, and both the oxidation reaction Mn&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;+¼O&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;(aq) + 3/2H&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O → βMnOOH (c) + 2H&lt;/span&gt;&lt;sub&gt;+&lt;/sub&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and the disproportionate reaction 2βMnOOH (c) + 2H&lt;/span&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;→ MnO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;(c) + Mn&lt;/span&gt;&lt;sup&gt;2+&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;+ 2H&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O can have positive reaction affinities. It is not possible for both reactions to be in thermodynamic equilibrium in the same system unless oxygen is almost completely absent. A value for Δ&lt;/span&gt;&lt;i&gt;G&lt;/i&gt;&lt;sub&gt;&lt;i&gt;f&lt;/i&gt;&lt;/sub&gt;&lt;sup&gt;0&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;of −129.8±0.6 kcal/mol was obtained for βMnOOH from experimental data by assuming that the reaction affinity for the oxidation reaction is equal to that for the disproportionation. A value for Δ&lt;/span&gt;&lt;i&gt;G&lt;/i&gt;&lt;sub&gt;&lt;i&gt;f&lt;/i&gt;&lt;/sub&gt;&lt;sup&gt;0&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;for βMnOOH of −129.8±0.5 kcal/mol was determined by measuring the redox potentials for the postulated half-reaction MnO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;(c) + H&lt;/span&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;+&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;i&gt;e&lt;/i&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;→ βMnOOH (c) at 0°, 5°, and 15°C and extrapolating to 25°C. Both these values are consistent with laboratory observations that βMnOOH is less stable than γMnOOH or Mn&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;O&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;at 25°C. Analytical data for manganese-depositing springwater samples are consistent with a nonequilibrium model involving disproportionation of either βMnOOH or Mn&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;O&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1029/WR018i003p00563</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>American Geophysical Union</dc:publisher>
  <dc:title>Stability of βMnOOH and manganese oxide deposition from springwater</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>