A Kinetic Model for Ion Exchange of Sodium from Lignite Using Sulfuric Acid

Date of Award


Document Type


Degree Name

Master of Science (MS)


Chemical Engineering


The removal of sodium from lignite by ion exchange techniques was studied using hydrogen ions from sulfuric acid. The exchange of calcium, magnesium, potassium, and aluminum from lignite was also observed. A measured amount of lignite and sulfuric acid solution was contacted in a beaker and stirred for a given period of time. The lignite and solution were then separated and analyzed to determine the extent of ion exchange. The lignite used contained 9.5 percent sodium oxide in the ash.

Five parameters were studied to determine their effect upon the exchange rate. These were initial H2S°4 concentrati°n / lignite particle size, stirrer speed, liquid (H2S04 solution) to solid (lignite) mass ratio, residence time.

The results of this work indicate that diffusion within the lignite particles was the rate controlling step. It was found that a decrease in the particle size, an increase in the residence time, and an increase in acid concentration cause an increase in the amount of sodium removed. The extent of sodium removal was predicted, quite precisely, by the following theoretically-based equation.

R = U (t) • X, R = percent sodium removed based on the initial sodium content, R is a function of t, r , and SO. anion concentration with constants o 4 D, and α, X = percent sodium removed at equilibrium = 93 percent for this work, U(t) = { 1 - exp [it2 ( ^ ( “JT + f2 (*)T2 + f3 («)T3 ) ] } 4, fl(oc) “ 0.570 + 0.430“: 1 0.775 f2 (a:) 0.260 + 0.782“ f3(‘^ 0.165 + 0.177“ T * V ^ V “ “ DA/DB where U(t) = the fractional attainment of equilibrium at t:Lme t + 2 D = diffusion coefficient of Na inside the particle, mm /min A + O D = diffusion coefficient of H inside the particle, mm /min rQ = the particle radius, mm t = the residence time, minutes The values of D and “ were found to be A 2 D = 0.0039 mm /min. A “ =exp[-0.6991*ln(SO^ anion concentration•2) - 1.8329] The SO^ anion concentration*2 is equal to the initial H2S04 acid solution concentration expressed in terms of normality

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