skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: A Simplified Gibbsite Solubility Equation for Modeling the Caustic Leaching of Aluminum-Bearing Sludge

Abstract

The Hanford Waste Treatment Plant (WTP) flowsheet includes an optional caustic leach step to remove gibbsite (Al(OH){sub 3}) from high-level waste sludge prior to vitrification. Aluminum leaching minimizes the mass that must be vitrified as high-level waste. The steady-state (time averaged) WTP flowsheet uses thermodynamic models that minimize Gibbs free energy to predict aluminum dissolution in the caustic leaching process, but these models are too computationally intensive to be solved in dynamic flowsheets. A gibbsite solubility model that is both accurate and rapidly solved by the.computer was needed and developed for a dynamic flowsheet. Available literature data on the solubility of gibbsite in aqueous sodium hydroxide solutions was compiled and the apparent equilibrium constant (Q) was calculated from the experimental data for each data point. The Q value is defined as the true equilibrium constant times the activity coefficients for the aluminate (Al(OH){sub 4}{sup -}) and hydroxide (OH{sup -}) ions in the reaction: Al(OH){sub 4}{sup {r_reversible}} Al(OH){sub 3(s)} + OH{sup -} The WTP dynamic flowsheet uses Q to determine the concentration of dissolved aluminate at equilibrium with gibbsite for a given hydroxide concentration. An empirical model to predict Q was developed by multi-linear regression of the experimentally determined Q valuesmore » from the literature. Four statistically significant model coefficients (all P statistics were less than 10{sup -25}) were identified: temperature, solution ionic strength, ionic strength squared, and a regression constant. This model was found to fit a large database of aluminum solubility data with an R{sup 2} of 0.98, which is comparable to the accuracy of more computationally intensive thermodynamic models for this data set. (authors)« less

Authors:
 [1]
  1. Washington Group International, 1779 Terminal Drive, Richland, WA 99354 (United States)
Publication Date:
Research Org.:
WM Symposia, Inc., PO Box 13023, Tucson, AZ, 85732-3023 (United States)
OSTI Identifier:
21208679
Report Number(s):
INIS-US-09-WM-06206
TRN: US09V0991079466
Resource Type:
Conference
Resource Relation:
Conference: Waste Management 2006 Symposium - WM'06 - Global Accomplishments in Environmental and Radioactive Waste Management: Education and Opportunity for the Next Generation of Waste Management Professionals, Tucson, AZ (United States), 26 Feb - 2 Mar 2006; Other Information: Country of input: France; 10 refs
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ALUMINATES; ALUMINIUM; ALUMINIUM HYDROXIDES; FREE ENTHALPY; GIBBSITE; HIGH-LEVEL RADIOACTIVE WASTES; LEACHING; Q-VALUE; RADIOACTIVE WASTE FACILITIES; RADIOACTIVE WASTE PROCESSING; REACTION KINETICS; SIMULATION; SODIUM HYDROXIDES; STEADY-STATE CONDITIONS; THERMODYNAMIC ACTIVITY; THERMODYNAMIC MODEL; VITRIFICATION

Citation Formats

Reynolds, J G. A Simplified Gibbsite Solubility Equation for Modeling the Caustic Leaching of Aluminum-Bearing Sludge. United States: N. p., 2006. Web.
Reynolds, J G. A Simplified Gibbsite Solubility Equation for Modeling the Caustic Leaching of Aluminum-Bearing Sludge. United States.
Reynolds, J G. Sat . "A Simplified Gibbsite Solubility Equation for Modeling the Caustic Leaching of Aluminum-Bearing Sludge". United States.
@article{osti_21208679,
title = {A Simplified Gibbsite Solubility Equation for Modeling the Caustic Leaching of Aluminum-Bearing Sludge},
author = {Reynolds, J G},
abstractNote = {The Hanford Waste Treatment Plant (WTP) flowsheet includes an optional caustic leach step to remove gibbsite (Al(OH){sub 3}) from high-level waste sludge prior to vitrification. Aluminum leaching minimizes the mass that must be vitrified as high-level waste. The steady-state (time averaged) WTP flowsheet uses thermodynamic models that minimize Gibbs free energy to predict aluminum dissolution in the caustic leaching process, but these models are too computationally intensive to be solved in dynamic flowsheets. A gibbsite solubility model that is both accurate and rapidly solved by the.computer was needed and developed for a dynamic flowsheet. Available literature data on the solubility of gibbsite in aqueous sodium hydroxide solutions was compiled and the apparent equilibrium constant (Q) was calculated from the experimental data for each data point. The Q value is defined as the true equilibrium constant times the activity coefficients for the aluminate (Al(OH){sub 4}{sup -}) and hydroxide (OH{sup -}) ions in the reaction: Al(OH){sub 4}{sup {r_reversible}} Al(OH){sub 3(s)} + OH{sup -} The WTP dynamic flowsheet uses Q to determine the concentration of dissolved aluminate at equilibrium with gibbsite for a given hydroxide concentration. An empirical model to predict Q was developed by multi-linear regression of the experimentally determined Q values from the literature. Four statistically significant model coefficients (all P statistics were less than 10{sup -25}) were identified: temperature, solution ionic strength, ionic strength squared, and a regression constant. This model was found to fit a large database of aluminum solubility data with an R{sup 2} of 0.98, which is comparable to the accuracy of more computationally intensive thermodynamic models for this data set. (authors)},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2006},
month = {7}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share: