Modeling cation exchange using EQ3/6

Conference · Sat Aug 01 04:00:00 EDT 1992

OSTI ID:139661

Viani, B ^[1]; Bruton, C; Bourcier, B

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1. Lawrence Livermore National Lab., CA (United States)

Geochemical modeling codes must be able to predict solid-solution and ion-exchange behavior of zeolites and smectites in order to design and assess strategies for containing and cleaning up toxic and/or radioactive wastes. Cation-exchange and solid-solution models have been implemented in the EQ3/6 geochemical modeling package and used to predict the composition of clinoptilolite under a variety of conditions. Published free energies of cation exchange on clinoptilolite at 25{degrees}C were combined with the calorimetric data for clinoptilolite to derive free energies of formation of the component end members of a solid solution in which mixing is allowed only on the exchange site. The solid-solution model and component end-member data were incorporated into EQ3/6 and its data base. An option to treat cation exchange independently of the solid-solution model was also developed and implemented in EQ3/6. This option allows the user to model mixed-phase exchangers, multisite exchangers, and systems in which the exchanger is not in overall equilibrium with the solution. Two {open_quotes}ideal{close_quotes} cation-exchange conventions [Vanselow (mole fraction) and Gapon (equivalent fraction)] are currently implemented in the code. A description of the cation-exchange models and their implementation into EQ3/6 is presented, and the relationship between the exchange formalisms and the solid-solution models is discussed. The advantages and limitations of the models and currently available thermodynamic data are addressed by comparing cation-exchange compositions of clinoptilolites with (1) published binary exchange data; (2) compositions of coexisting clinoptilolites and formation waters at Yucca Mountain; and (3) experimental sorption isotherms of Cs and Sr on zeolitized tuff.

• Research Organization: Los Alamos National Lab., NM (United States)
• OSTI ID: 139661
• Report Number(s): LA--12325-C; CONF-9009350--; ON: DE92041241
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
54 ENVIRONMENTAL SCIENCES
CATIONS
CESIUM
CLINOPTILOLITE
E CODES
ENVIRONMENTAL TRANSPORT
ION EXCHANGE
RADIOACTIVE WASTE DISPOSAL
SMECTITE
SOLID SOLUTIONS
SORPTION
SORPTIVE PROPERTIES
STRONTIUM
TUFF
UNDERGROUND STORAGE
WASTE-ROCK INTERACTIONS
YUCCA MOUNTAIN
Yucca Mountain Project
ZEOLITES