Production of biochar from spent tea waste and hazelnut shells, characterization and its use for the preconcentration of some heavy metals

In this thesis study, novel solid-phase extraction (SPE) methods were developed for separation and preconcentration of trace levels of Cd(II), Pb(II), Ni(II) and Co(II) ions from environmental water samples prior to their determination by Flame Atomic Absorption Spectrometry (FAAS). Within this scope, biochars were produced via pyrolysis from low-cost biomass sources, namely spent tea waste and hazelnut shell. Subsequently, spent tea waste biochar (DÇAB) and hazelnut shell biochar (FKB) were modified with magnetic nanoparticles to synthesize new magnetic composite adsorbents. The structural and surface properties of the synthesized adsorbents were characterized using various instrumental techniques. Experimental parameters affecting adsorption and desorption efficiencies, including solution pH, adsorbent dosage, contact time and the type and concentration of the desorption solution were optimized for the DÇAB/Fe3O4 adsorbent using a Central Composite Design (CCD) approach. Furthermore, an Artificial Neural Network (ANN)-based model was developed to predict percentage recovery using the experimental data obtained. For the DÇAB/CoFe2O4 and FKB/NiFe2O4 adsorbents, optimization studies were carried out using a one-variable-at-a-time (OVAT) approach. The analytical performance of the developed method was assessed based on enrichment factor (EF), relative standard deviation (RSD), limit of detection (LOD) and limit of quantification (LOQ). The maximum adsorption capacities of the synthesized adsorbents were determined using the Langmuir isotherm model. Accordingly, the adsorption capacity of DÇAB/Fe3O4 for Cd(II) was found to be 79.4 mg g-1; for DÇAB/CoFe2O4, the capacities for Cd(II), Pb(II) and Ni(II) were 69.4, 185.2 and 45.2 mg g-1, respectively; and for FKB/NiFe2O4, the capacities for Cd(II), Pb(II) and Co(II) were calculated as 20.4, 28.2 and 21.7 mg g-1, respectively. The accuracy and reliability of the developed method were demonstrated through spike/recovery tests performed on different environmental water samples.