Abstract
Industrialization has introduced heavy metals into the environment and water bodies, causing severe toxicity to humans, animals, and the environment; thus, the heavy metals need to be monitored and controlled. This study investigated the capacity of peanut shell (PS)-derived biochar to extract lead and chromium from synthetic wastewater based on the key parameters that affect adsorption such as adsorption temperature, adsorption contact time, pre-treatment, initial metal concentration, and adsorbent particle size. Design Expert 13 software was used for determining the number of experimental runs and ANOVA analysis for lead and chromium extraction studies. Peanut shells were crushed and sieved into different particle sizes (250 â 500 ðð), pretreated with formalin (1:5), and pyrolyzed at a temperature of 565â for 3.75 hours. The PS biochar was mixed with lead and chromium synthetic wastewater solutions individually at initial metal concentrations of 50, 75, and 100 ppm in an orbital thermal shaker at adsorption temperatures of 15, 25, and 35 â. After adsorption, the biochar was separated from the solution using filters and analyzed using the Atomic Absorption Spectrometer (AAS). The experimental data from the AAS was used to determine the optimum conditions in Design Expert 13 and for building and validating predictive models in JMP pro 13 statistical software using the ANN models for the chromium and lead extraction studies. The ultimate, core and proximate analyses were conducted in this research study for characterization purposes, the proximate analysis was conducted using a dryer for moisture content & a muffle furnace to determine the ash & volatile matter contents and for the ultimate analysis a PerkinElmer Elementar CHNS analyzer was used to determine the elemental composition of the raw-, pretreated- PS and PS-derived biochar. In addition to the ultimate and proximate analyses, the characterization of raw PS, pre-treated PS and PS-derived biochar was conducted through core (SEM, FTIR, XRF and XRD) analysis. The study found that lead
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extraction decreased with an increase in pH and initial metal concentration, while chromium extraction decreased with an increase in adsorption temperature and adsorbent particle size till 385 Ξm. The optimum parameters for lead and chromium extractions were at concentrations of 88.37 & 86.54 ppm, adsorption temperature of 15.52 & 24.55 â, adsorption contact time of 30.37 & 32.95 minutes, adsorption particle size of 285.24 & 401.78 Ξm, and pH of 2.69 & 5.96 with 98.39% & 92.92% extraction, respectively. It was found the Langmuir adsorption isotherm model best fitted the lead and chromium (both) extraction studies with ð
2 of 0.996 and 0.999, respectively. The ANOVA analysis of both studies showed that the experimental data is significant and can be used for prediction applications and it was found that the 5-node ANN simulation model best fitted both studies. This research study was based on a circular economy approach with the usage of waste which were the peanut shells as feed to the wastewater treatment process, and instead of discarding the waste thus after adsorption, the biochar can be regenerated by desorbing the adsorbed heavy metals from the impregnated adsorbent (biochar) and furthermore the regenerated biochar can be reused in the wastewater treatment or for mulching in agriculture. The desorbed chromium and lead ions can be sold thus minimizing the waste generated in a process and also mitigating the environmental and water pollution. The circular economy approach in this study ensured a safe, reliable, inexpensive, and easy-to-operate process to clean heavy metal-contaminated water using readily available, cheap, and accessible adsorbents. The study did not focus on peanut shell-derived biochar regeneration but recommends it.