Algal-derived biochar as an efficient adsorbent for removal of Cr (VI) in textile industry wastewater: Non-linear isotherm, kinetics and ANN studies

Textile industries release effluent that contains the vast majority of heavy metals in which Cr (VI) is a toxic carcinogenic element that causes an environmental problem. The aim of the work is to synthesize algae-derived biochar derived from algae using slow pyrolysis at an operating temperature of 500 °C, a heating rate of 10 °C/min and a residence time of 60 min and to use it as an adsorbent to remove Cr (VI). The batch experiment was carried out using different concentrations of Cr (VI) (1, 10, 25, 50, 100, 125, 150 and 200 ppm) at different intervals of time (2.5, 5, 10, 15, 30, 60, 120 and 240 min). The maximum removal percentage of Cr (VI) is 97.88% for the metal concentration of 1 ppm exhibiting non-linear adsorption isotherm (Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin models) and kinetic models (pseudo-first order, pseudo-second order, nth order, and intra-particle diffusion) were analyzed using a solver add-in of Microsoft Excel. According to the results, the Langmuir isotherm model (R² = 0.999) and pseudo-nth order models are suitable to describe monolayer adsorption and the process kinetics, respectively. The maximum adsorption capacity of algal biochar to adsorb is 186.94 mg/g. For the prediction of the optimal removal efficacy, an artificial neural network of the MLP-2-7-1 model was used. The results obtained are useful for future work using algal biochar as an adsorbent of Cr (VI) from textile wastewater to achieve sustainable development goals.