Boron removal and recovery with electrocoagulation process and iron oxide particles assisted by high gradient magnetic separation process

The treatment of water containing boron is a very interesting area of research that has been the subject of several studies in recent years. This is due to the increasing harmful effects of boron traces in water streams on the environment and human health, as well as the global demand for boron in various industries, coinciding with the implementation of stricter water quality standards. Boron is used in a wide range of industrial processes and is referred to as the "salt of industry". There are more than 200 varieties of this element in nature, but only a small fraction of them are of commercial importance, which has led to the scenario that it should be operated in a sustainable cycle. It is well known that no element in nature is available in unlimited quantities. With the increase in demand, the principle of sustainability, which must be present at every stage of the developing production processes, has made the recovery of precious metals a necessity today due to the limited availability of raw materials. In the current framework, there is a need for new technologies required for this process, which are expected to be sustainable in themselves. In this context, the electrocoagulation (EC) process using Fe (iron) electrodes and the adsorption process using iron oxide nanoparticles (IONP) were investigated separately for the treatment of boron wastewater. These systems were also subjected to magnetic separation for solid-liquid phase separation and a hybrid process was designed using a high gradient magnetic separator (HGMS). The effect of operating parameters such as pH, current density, electrolysis time on boron removal by EC process was investigated. The Box-Behnken statistical model was used in the optimization study. According to the results obtained, the optimum pH value was determined to be 10,94, the optimum electrolysis time was determined to be 60 min, and the optimum current density was determined to be 1,06 A/m2 for wastewater with boron concentration of 1000 mg/L in the EK process using Fe-electrode. In the adsorption process, the optimum pH value at which the boron removal was the highest was determined to be 11, the optimum reaction time was 120 minutes, and the optimum amount of IONP was determined to be 0,2 grams (603 mg/g). The adsorption process using IONPs, 0.-1.-2. order reaction kinetics and the structures of the reactions using Langmuir, Freundlich isotherm models were explained. The optimum values of the processes whose optimum values were determined, and the optimum values of the HGMS process developed for liquid-solid phase separation were determined separately. The optimum separation time was 180 minutes, optimum flow rate was 0,64 L/min, optimum current density was 1,3 A/m2-7600 G for EC+HGMS hybrid process, while the optimum separation time was 75 minutes, optimum flow rate was 0,64 L/min, optimum current density was 0,1 A/m2-700 G for adsorption with IONP+HGMS hybrid process. SEM, EDS analyses of the boron minerals recovered after hydrothermal mineralization method were carried out to determine the removal mechanisms of each process and to obtain recovery. Under the optimized conditions, the R2 (regression) value for boron removal in the EC process using Fe electrodes was determined to be 0,96. The fact that R2 and R2adj values are close to 1 shows that the experimental results and statistical data are compatible and that the Box-Behnken statistical model plays an effective role in determining the process parameters. In the adsorption process using IONPs, the adsorption reactions can be explained by the first-order kinetic model and the Freundlich isotherm model. The removal efficiencies of EC and IONP adsorption processes are very close to each other. While pH and electrolysis time are very effective parameters for EC, pH, reaction time and adsorbent amount are effective parameters for IONP adsorption. In the hybrid systems, although the flow rate is common for both processes, the current density applied to the system to generate the magnetic field is quite low for IONP adsorption+HGMS, while it is higher for EC+HGMS process. This can be explained by the high sensitivity of IONPs to the magnetic field. In the light of the results obtained in the study, these systems, which are quite advanced in applicability and efficiency compared to conventional methods, are also open to development and new areas of use. While the phase separation of spinel ferrites formed as a result of the EC process with the help of a magnetic field is one of the most important originality stages, the regeneration and reusability of the IONPs used for the adsorption process adds a unique meaning to the study and supports the principle of sustainability while providing raw material control. The positive difference in the efficiencies obtained with the integration of the HGMS process, which is the biggest differential separation of the process, has given a new breath to the liquid-solid phase separation stage in water/wastewater treatment.