The recovery of boron from borax sludge by solid−liquid extraction was investigated using 23
factorial experimental design. Distilled water and sulfuric acid were used as extraction solvents.
The effects of solid-to-liquid ratio, reaction time, and reaction temperature were investigated
for extraction with distilled water. The effects of solid-to-liquid ratio, reaction time, and solvent
concentration were investigated for extraction with sulfuric acid. The interaction among the
operating parameters and their relative significance were studied. Regression equations were
established for both solvents, and the extraction was represented as a function of response
variables. The accuracy of equations was verified by Fisher's adequacy test. It was found that
the most effective parameter for the extraction process was solid-to-liquid ratio for both of the
solvents. Maximum boron oxide extraction efficiency was obtained under the following working
conditions: solid-to-liquid ratio, 1/120 g/mL; reaction time, 60 min; reaction temperature, 75 °C
for distilled water; and solid-to-liquid ratio, 1/120 g/mL; reaction time, 60 min; solvent
concentration, 1%, v/v; reaction temperature, 75 °C for sulfuric acid.
A two-step process for boron recovery from clay waste is proposed in the present work. The leachate obtained after the clay waste was leached with sulphuric acid solution was treated with Diaion CRB-02 - a boron-specific resin for the separation of boron from the alkaline species in the leachate. The batch studies showed that a maximum boron recovery of about 95% was obtained at a pH value of 8.0, an initial boron concentration of 50 mg L(-1), a contact time of 24 h and a temperature of 25 degrees C. Equilibrium sorption data fitted the Langmuir isotherm. Column studies were carried out using different inlet boron concentrations and flow rates at a pH value of 8.0 and a temperature of 25 degrees C. The Yoon-Nelson and Thomas models were used to describe the dynamic behaviour of the column and to determine the column kinetic parameters. By these models and graphical integration, the column capacity values were found to be 7.3-8.5 mg g(-1) and 7.1-8.5 mg g(-1), respectively, and the 50% breakthrough time values were found to be 21-155 min and 19-149 min, respectively, depending on the inlet concentration and flow rate. It was observed that about 76% of the boron in the leachate solution could be recovered at an inlet boron concentration of 250 mg L(-1), a flow rate of 2.5 mL min(-1), a pH value of 8.0 and a temperature of 25 degrees C.
The dissolution kinetics of sepiolite in hydrochloric acid and nitric acid were studied in a batch reactor. The effects of reaction temperature, acid concentration, particle size and solid-to-liquid ratio on the dissolution process were investigated. Experimental studies were carried out in the ranges of 25À75ºC for reaction temperature, 0.25À1.00 mol/L for acid concentration, 0.00755À0.05020 cm for average particle size and 2.5 to 12.5 g of solid/100 mL of acid for solid-to-liquid ratio. It was determined that the dissolution process is controlled by resistance of the diffusion through the product layer. The activation energies of the process were determined to be 40.8 and 38.3 kJ/mol for hydrochloric and nitric acid, respectively. The apparent rate constants were expressed as a function of reaction temperature, acid concentration, particle radius and solid-to-liquid ratio: kae À4 9 1 0 ( 1 / T ) Cr À0 . 6 (s/l) À1 and kae À4606(1/T) Cr À0.5 (s/l) À1 for hydrochloric and nitric acid, respectively; k is the apparent rate constant in min À1 ; T, the reaction temperature (K); C, the acid concentration (mol/L); r, the initial particle radius (cm); s/l, the solid-to-liquid ratio (g of solid/100 mL of acid).
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