Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1900. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed Oct. 28, 2008). Includes bibliographical references.

This project focused on aluminum precipitation within the Caustic Side Solvent Extraction (CSSX) process at the Savannah River Site (SRS). The CSSX process uses a solvent to separate cesium. In the scrubbing section, the solvent containing cesium is scrubbed with 0.05 M nitric acid to remove soluble sodium and potassium ions. During scrubbing, aluminum precipitation has been observed. Solids precipitation is of concern as solids might erode centrifugal contactor internals and/or plug transfer pipelines. Hence, it is important to identify conditions under which solids precipitation may occur and identify an operating region where solids precipitation is minimized. Room temperature experiments on the CSSX scrubbing process were conducted. Experimental results were compared with predictions from ESP (Environmental Simulation Program). The order and specific rate for the reversible aluminum precipitation reaction were obtained as a function of initial stream dilution and % carryover. The reaction was first order based on regression results.

Poor settling of solids increases land requirement for tailings containment and imposes severe constraints on the water balance. Consequent to these considerations, the alternating current electrocoagulation (AC/EC) technique emerged as a candidate for enhancing the settling behaviour of suspensions in the mineral, coal and oil sands industries. Hence, a fundamental study of AC/EC was undertaken with aluminum electrodes. Ground silica (d50 = 20 m), which formed a stable suspension, served as the model tailings solid at 5.0 wt % in water. The AC/EC process consisted of two developmental stages: coagulation, marked by pH decrease in the silica suspension; and floc growth, characterized by pH increase from the minimum (i.e., the end of coagulation). AC/EC enhanced the initial settling rate of silica by over three orders of magnitude, and exhibited remarkable flexibility by virtue of the wide range of process parameters that could be optimized. For example, AC/EC can be operated in either the indirect or direct mode. The settling behaviour of bentonite (estimated d50 < 1 m) was more enhanced by indirect AC/EC, while that of silica benefited more from direct AC/EC. Any condition that increased aluminum dosage (e.g., current, retention time), increased the initial settling rate of silica. Over the feed water pH range of 3.0 to 9.1, AC/EC was effective in enhancing the settling behaviour of silica. AC/EC was also effective over a wide range of temperatures (23 to 85C). High electrical energy demand by AC/EC was observed throughout this study. Its optimization was beyond the scope of this work. Dilution of a sample of Syncrude mature fine tailings (MFT) to 4.6 wt % solids sustained a stable suspension. Settling occurred after AC/EC treatment, a crystal-clear supernatant resulted and bitumen was recovered as froth. Entrained solids were easily spray-washed from the froth with water. The settling behaviour of a Luscar Sterco fine coal tailings sample was not augmented by AC/EC, possibly due to contamination by the companys own electrocoagulation operation. After having been stored dry for more than a year, electrocoagulated silica was an effective coagulant for as-received silica and Syncrude MFT. / Chemical Engineering

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