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<p><a href="page.php?w=soda_ash">soda ash</a>, or caustic soda (<a href="page.php?w=sodium_hydroxide">sodium hydroxide</a>) can be added to raise the pH during water purification processes and is especially common practice for <a href="page.php?w=water_softening">water softening</a>. The choice of chemical used for raising the pH often depends on the carbonate alkalinity in the water. Addition of such chemicals increases the carbonate ion concentration, forcing precipitation of <a href="page.php?w=calcium_carbonate">calcium carbonate</a>, and <a href="page.php?w=magnesium_carbonate">magnesium carbonate</a></p><p>
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