Effect of soluble calcium on the determination of the labile metal content of sediments with ion-exchangers.
Equilibration of sediments with cation-exchangers results in a transfer of loosely bound labile metal species to the exchanger phase. Dissolution of the matrix is also promoted and selectivity rules suggest that some of the cations released (particularly Ca) could effectively compete with metal ions for exchange sites. This potential source of error has been evaluated by studying synthetic mixtures of Ca(2+) and other metal ions (Cu(2+), Pb(2+), Cd(2+), Zn(2+)) and by analysis of two calcium-rich wastes (a calcine and a jarosite). The ion uptake most influenced by calcium competition was that of zinc; uptake of lead was least affected. For minimum error, i.e., optimum transfer of "available" or "labile" metal ion, the level of free Ca(2+) introduced into the solution should not exceed 300 mg/l., and the amount of exchanger added must provide an excess of exchange sites relative to the amount of cations released from the sample. By use of exchangers of different types it is possible to attempt some classification of the labile metal content, e.g., acid-displaced, exchangeable, salts of weak acids.
Beveridge
A
A
Chemistry Department, University of Newcastle, NSW 2308, Australia.
Waller
P
P
Pickering
W F
WF