Adsorption of Molybdate Anion (MoO₄²⁻) by Sodium-Saturated Kaolinite

Abstract

Abstract Adsorption of Mo(VI) on 2-0.2- μ m size fraction of sodium-saturated kaolinite at 25 ± 2°C and at a constant pH of 7.00 ± 0.05 was studied. The kaolinite sample was pretreated to remove any surface oxide and hydroxide coatings. The initial concentrations of Mo in solution ranged from 1 to 11 mg/liter in a NaClO 4 background electrolyte at a constant ionic strength of 0.09 ± 0.01. Calculations of speciation using the GEOCHEM computer program indicated that under experimental conditions Mo(VI) was mainly in the MoO 4 2− form. The experimental conditions were also shown to fulfill the requirements for applying the Langmuir equation in interpreting adsorption data. The Langmuir parameter for the adsorption maximum, n°, and the affinity parameter, <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content"><mml:msub><mml:mi>K</mml:mi><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi>M</mml:mi><mml:mi>o</mml:mi><mml:msub><mml:mi>O</mml:mi><mml:mrow class="MJX-TeXAtom-ORD"><mml:msup><mml:mn>4</mml:mn><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>2</mml:mn><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:msub><mml:mo>−</mml:mo><mml:mi>C</mml:mi><mml:mi>l</mml:mi><mml:msub><mml:mi>O</mml:mi><mml:mrow class="MJX-TeXAtom-ORD"><mml:msup><mml:mn>4</mml:mn><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:msub></mml:mrow></mml:msub></mml:math> were computed to be 3.33 × 10 −4 mole/ mole of adsorbent and 5.969 × 10 5 , respectively. The large affinity parameter indicated that the Na-saturated kaolinite surface has a very high affinity for MoO 4 2− ions relative to ClO 4 − ions.