Reusing menengic (Pistacia terebinthus) coffee waste as an adsorbent for dye removal from aqueous solution

The aim of this study is to characterise a bio-waste natural material and investigate its reuse for other purposes. Menengic (Pistacia terebinthus) coffee bio-waste (MCW) was characterised and used to remove malachite green oxalate (MGO) and methylene blue (MB) from aqueous solutions. Characterisation of adsorbent was performed with Brunauer-Emmett-Teller method, Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction techniques. Adsorption parameters such as pH, amount of adsorbent, contact time, mixing speed, initial dye concentration, and temperature were investigated by classical batch adsorption process. Maximum dye adsorption (99.59 +/- 0.05% for MGO and 96.54 +/- 0.21% for MB) onto MCW were observed at pH values of 8 and 6, and 150 mg and 200 mg of adsorbent in 200 mg/L dye solution at 25 degrees C for 45 min with a mixing speed of 400 rpm, respectively. In this context, Langmuir, Freundlich and Temkin isotherms were tested and it was found that the most suitable isotherm for the experimental data was the Langmuir isotherm with an R-2 value of 0.9915 for MB and 0.9852 for MGO. In addition, the maximum adsorption capacity for MGO and MB was determined as 59.17 mg/g and 32.68 mg/g, respectively. The adsorption characteristics of MGO and MB indicate that they coincided with pseudo-second-order kinetics. According to this kinetic model, the mechanism is compatible with chemisorption as the rate determination step and the thermodynamic data suggested the spontaneous and exothermic process.

Automated summary

The aim of this study is to characterise and explore the reuse of a bio-waste natural material. It was found that the material had high adsorption capacity for malachite green oxalate and methylene blue under certain conditions. The suitable isotherm model and kinetic model for the adsorption process were determined.