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15
CH3041
AQUATIC ION
EXCHANGE
• Cation Exchange Capacity (CEC), the ability of
a solid to sorb cations, is an important
variable in sediments and colloids due to the presence of clay minerals.
• CEC depends on pH & salt concentration.
• CEC is usually determined by replacing all
exchangeable sites in the solid with NH4+.
exchangeable sites in the solid with NH4+.
• Metal cations
that can be exchanged :
Na+, K+, Ca2+, Mg2+, Fe2+, Mn2+, Cu2+, Ni2+.
Na+, K+, Ca2+, Mg2+, Fe2+, Mn2+, Cu2+, Ni2+.
• The rest of the
CEC is exchangeable H+.
• Freshwater sediment CEC 20-30 cmol/kg.
1 cmol(+)/kg = 1 meq/100g
1 cmol(+)/kg = 1 meq/100g
• Sediments offer
the ability to act as pH
buffers and metal repositories thru the CEC.
buffers and metal repositories thru the CEC.
