Effect of sorption on Co (II), Cu (II), Ni (II) and Zn(II) ions precipitation

The precipitation of divalent metal cations Cu (II), Zn (II), Co (II) and Ni (II) with KOH solutions is measured as a function of pH and temperature. The precipitation of divalent metal cations is studied with and without Al(OH)3. The shift of the titration curves at a given temperature in the presence of adsorbent is related to the metal ions adsorption (at the pH values) below plateau. The order of precipitation of the divalent metal cations is found to be in the order Cu (II) > Zn (II) > Co (II) > Ni (II) which is parallel to the values of their solubility products. The negative values of ΔHº indicate the precipitation process to be exothermic, while the positive values of ΔSº show a net disordering of the system on account of the loss of the water of hydration. The negative values of ΔGº are well correlated with the favorable nature of precipitation process.

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► Precipitation of metal cations follows order Cu (II) > Zn (II) > Co (II) > Ni (II).
► Negative ΔHº values indicate the precipitation process is exothermic.
► The values of ΔGº demonstrate the favorable nature of precipitation process.