Effects of process variables namely pH, dye concentration, adsorbent dosage, temperature, particle size
and agitation speed on kinetics of methylene blue adsorption onto gulmohar plant leaf powder were
investigated. Quadratic models were proposed to predict pseudo second order rate constant and equilibrium
uptake in terms of the process variables. Model coefficients were determined by multiple regression
analysis. Statistical tools like Student’s t-test, F-test, ANOVA and lack-of-fit were used to define the most
important process variables. The proposed models could predict the rate constant and equilibrium dye
uptake with high R2 values (0.94 and 0.947). It was found that rate constant increased with decrease in
concentration, decrease in particle size, increase in adsorbent dosage, increase in agitation speed and
increase in temperature. Meanwhile, it was found that equilibrium dye uptake increased with increase in
concentration and decrease in dosage. Apart from these combined effects of the process variables were
established through multiple regression analysis. Langmuir monolayer adsorption capacity of GUL was
found to be 186.22 mg/g.