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The kinetics of leaching of calcined magnesite by citric acid solution was studied. The effects of reaction temperature, particle size, and acid concentration were investigated. The leaching data showed that the reaction is under chemical kinetics control with an activation energy of 39.1 kJ mol -1 . Additionally, the fact that leaching was controlled by the chemical reaction was also supported by the relationship between the rate constant and the particle radius.

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The adsorption of Malachite Green onto natural red clay by batch‐adsorption technique is investigated. The effects of initial dye concentration, amount of adsorbent, adsorption time, pH, and temperature are examined. The results of X‐ray diffraction, scanning electron microscopy, Thermogravimetry/Differential Thermal Analysis, Brunauer–Emmett–Teller Surface Area Analysis, and Harkins‐Jura Pore Size ‐ Volume Analysis are used for the characterization of adsorbent. The adsorption capacity, isotherm, kinetics, and equilibrium studies are performed. The maximum adsorption has occurred at pH ranging from 6.0 to 10.0. Therefore, the free pH value of 5.16 is chosen as the constant parameter. The pseudo second order kinetic model is found to be in good agreement with the experimental values obtained. The adsorption equilibrium data are analysed using various adsorption isotherm models and the results show that adsorption behavior fits well to the Freundlich isotherm model. The maximum monolayer adsorption capacity is found to be 84.75 mg/g. From the positive values of ∆Ho and the negative values of ∆Go, it can be said that adsorption processes are carried out with endothermic, physical adsorption, and spontaneous.