The aim of this study was to investigate heavy metal removal using waste biomass adsorbent, persimmon leaves, in an aqueous solution. Persimmon leaves, which are biomaterials, have a large number of hydroxyl groups and are highly suitable for removal of heavy metals. Therefore, in this study, we investigated the possibility of removal of Cu, Pb, and Cd in aqueous solution by using raw persimmon leaves (RPL) and dried persimmon leaves (DPL). Removal of heavy metals by RPL and DPL showed that DPL had a 10%e15% higher removal than RPL, and the order of removal efficiency was found to be Pb > Cu > Cd. The pseudo-second order model was a better fit to the heavy metal adsorption experiments using RPL and DPL than the pseudo-first order model. The adsorption of Cu, Pb, and Cd by DPL was more suitable with the Freundlich isothermal adsorption and showed an ion exchange reaction which occurred in the uneven adsorption surface layer. The maximum adsorption capacity of Cu, Pb, and Cd was determined to be 19.42 mg/g, 22.59 mg/g, and 18.26 mg/g, respectively. The result of the adsorption experiments showed that the n value was higher than 2 regardless of the dose, indicating that the heavy metal adsorption on DPL was easy. In the thermodynamic experiment, DG
was a negative value, and DH
and DS
were positive values. It can be seen that the heavy metal adsorption process using DPL was spontaneous in nature and was an endothermic process. Moreover, as the temperature increased, the adsorption increased, and the affinity of heavy metal adsorption to DPL was very good. This experiment, in which heavy metals are removed using the waste biomass of persimmon leaves is an eco-friendly new bioadsorbent method because it can remove heavy metals without using chemicals while utilizing waste recycling.

Introduction

Wastewater produced in industrial processes generally contains inorganic contaminants and organic toxicants (Choi, 2015a). In particular, various compounds including cadmium, lead, copper, and chromium have been widely used in the chemicals industry and in the finishing processes in metals and mining. These heavy metal pollutants can cause physical and chemical changes in the water environment, altering the quality of the water environment, and the use of contaminated water can have a crucial negative impact on living organisms (Choi et al., 2016). Especially, cadmium (Cd) and lead (Pb) are harmful contaminants that can have a detrimental effect on living organisms even with small accumulations (Abdelfattah et al., 2016). Cd is a toxic heavy metal commonly present in wastewater and is very toxic. While Pb is less toxic than cadmium, it is one of the heavy metals most commonly used in industrial processes, and is therefore one of the most abundant heavy metals in wastewater (Choi, 2015b; Taty-Costodes et al., 2003). Pb has a high affinity for enzymes, phosphate ions (PO4 3), ligands, and biomolecules including thio (eSH) which affect the membrane permeability of the kidneys, liver, and brain, thereby inhibiting biosynthesis of the cells in vivo (Chen et al., 2010). It also complexes with the oxo-groups of enzymes that influence the stages of hemoglobin synthesis and porphyrin metabolism, resulting in peripheral and central nerve toxicity, renal toxicity, and digestive disorders (Kabbashi et al., 2009). Copper (Cu) is one of the dangerous heavy metals used in many industries such as mining and smelting, plating, brass manufacturing, petroleum refining, and electroplating, and is used in Cu based pesticides (Sengil and Ozcar, 2008). The released copper is not decomposed by microbial activity in the natural environment and causes a serious delayed action on the activity and decomposition of organic matter (Kim et al., 2015). Low levels of copper are found as minerals essential for the catalytic activity of enzymes in organisms, but excessive copper intake accumulates in the liver causing gastrointestinal problems, kidney damage, and anemia, and the higher the concentration, the greater the potential toxicity to the organism (Li et al., 2006; Murugesan et al., 2011). Accumulation of Cu, Pb, and Cd in the human body causes gastrointestinal problems, kidney damage, and anemia etc., and is more potentially toxic at higher concentrations, leading to death (Ali et al., 2016; Barsbay et al., 2017). The International Agency for Research on Cancer (IARC) classified Cu, Pb, and Cd as carcinogens, and the World Health Organization (WHO) regulates the release of Cd, Pb, and Cu to be less than 0.003 mg/L, 0.01 mg/L, and 2 mg/L, respectively (Choi et al., 2016). Therefore, these toxic heavy metals need to be removed before they are released into the water system.