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

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Abstract
Adsorption of Mo(VI) on 2-0.2-um size fraction of sodium-saturated kaolinite at 25 _+ 2~ 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 NaC104 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 MoO4 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, KMoO,2 -ao, were computed to be 3.33 x 10 -4 mole/ mole of adsorbent and 5.969 x 105, respectively. The large affinity parameter indicated that the Na- saturated kaolinite surface has a very high affinity for MoO42 ions relative to C10 4- ions.

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