Statistical optimization, soft computing prediction, mechanistic and empirical evaluation for fundamental appraisal of copper, lead and malachite green adsorption

Abstract

This paper describes an efficient and low cost material for treatment of Cu²⁺, Pb²⁺ and malachite green from aquatic environments. Aerated Autoclave Concrete (AAC) was used as a low cost bed and modified by chitosan to synthesize of AACCH composite. Then, it was analyzed by the Energy Dispersive X-ray spectroscopy (EDX), X-Ray Fluorescence (XRF), Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier Transform Infrared spectrophotometry (FT-IR) analysis. The key factors influencing on the removal percentage among each run including, sample's pH, amounts of adsorbent and contact time were optimized by the Central Composite Design in Response Surface Methodology (CCD-RSM). Based on the obtained results, the optimum conditions for the removal of both Cu²⁺ and Pb²⁺ are pH 5.8, amounts of adsorbent: 14 mg and 58 min contact time. Also, for MG, its maximum removal percentage obtained at pH 9.7, 13 mg adsorbent and 55 min removal time. In addition, the variations of adsorptive behaviors were scrutinized by Adaptive Network-based Fuzzy Inference System (ANFIS) based on Sugeno model with focusing on removal percentage predictions. Also, to evaluate the adsorption mechanism, Dubinin–Radushkevich (D-R), Langmuir, Temkin, Freundlich (two parameter equations) and Sips, Khan and Toth isotherms (Three parameter equations) were appraised and the outcomes demonstrate that the adsorptive reaction of Pb²⁺, Cu²⁺ and MG governed by the Freundlich isotherm with the maximum adsorption capacities of 78.12, 56.82 and 833.33 mg g⁻¹, correspondingly. Likewise, outputs of the D-R and Temkin isotherms show that the physiosorption process is the main interaction of analytes with AACCH composite. The consequences of the kinetic modeling illustrated that the adsorptive reaction of Cu²⁺, Pb²⁺ and MG followed by the pseudo second order adsorption kinetic. The geometry kinetic computing depicted that the adsorption/desorption rates don't have any interfering during reaction process. The advantages such as high efficiency, low cost, reusability and green aspect, make AACCH composite as a high performance adsorbent for decontamination of Pb²⁺, Cu²⁺ and MG from water resources.

Introduction

Environmental pollution is one of the main threaten of human and animal health in the century 21. By developing of technologies, application of heavy metals in different fields increases dramatically. Lead (Pb) has widespread applications in batteries, alloys, pigments and cable sheathing [[1], [2]–3]; Copper (Cu) is the most applicable heavy metal with wide applications in electrical wire, industrial machinery, alloys, medicine, kitchenware and etc. [4]. Copper is an important constituent of enzymes and proteins responsible for growth, cardiovascular integrity, lung elasticity, neovascularization, neuroendocrine function, and iron metabolism [5]. At very high concentrations, it causes gastrointestinal mucosal ulcerations and bleeding, acute hemolysis and hemoglobinuria, hepatic necrosis with jaundice, nephropathy with azotemia and oliguria, cardiotoxicity with hypotension and central-nervous-system (CNS) manifestations (e.g., dizziness, headache, convulsions, lethargy, stupor, and coma) [5]. Also, in adults, Pb causes problems of the peripheral and central nervous systems, kidneys (e.g., renal failure), and reproductive organs (e.g., decreased sperm count) [5]. Malachite Green (MG) is an organic cationic dye using as an antibacterial agent. Its presence in water samples absorbing sunlight and disturbing the photosynthesis process of seaweeds. Therefore, the concentration of dissolved oxygen reduces which could be cause to the death of aquatics [6, 7]. Due to the high toxicity of lead and copper ions at high levels and also carcinogen effect of MG and other organic dyes for humans; their removal from water samples is highly demanded [[8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]–21]. Among the analytical procedures for treatment of pollutants from aquatic environments; adsorption technique has great attendance due to its unique specifications such as spread variety of adsorbents, reaction speediness, simplicity of the procedure, low cost and ability to use of the adsorbent by its recovery [[22], [23], [24], [25]–26]. Aerated autoclave concrete (AAC) is one of the lightweight materials which consist of silica, sand, portland cement type 2, lime, quartz and aluminum powder [27]. Since light-weight materials reduce the weight of the structures, these compounds become great significance in constructions; therefore, they are suitable to replace with traditional bricks. Due to their widespread application in Iran, their waste also increases and it is more necessary to consider them for reutilization according to the integrated solid waste management (ISWM) [28].

Chitosan is an amino polysaccharide which produced from chitin by alkali deacetylation [29]. It has antibacterial properties and used as a natural antimicrobial agent in the cosmetic pharmaceutical, agricultural, and food industries. Moreover, because of different amino and hydroxyl compounds in its composition, biocompatibility and non-toxicity, it has been utilized for refining contaminations form water resources [30, 31]. Herein, aerated autoclave concrete coated chitosan (AACCH) composite has synthesized as a cost effective, high efficient and rapid adsorbent for the removal of Pb²⁺, Cu²⁺ and MG. AAC powder was used as a bed and chitosan coated on its surface to synthesize AACCH composite. The hydrogen bonding interaction of chitosan (N−H and O−H) with OH and Si-O-Si groups of AAC adsorbent is the main interaction between chitosan and AAC. The synthesized adsorbent was characterized by the Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared spectrophotometry (FT-IR), X-Ray diffraction analysis (XRD), Energy Dispersive X-Ray spectroscopy (EDX) and Brunauer–Emmett–Teller (BET) analysis. The parameters such as sample's pH, amounts of adsorbent and contact time were thoroughly investigated by the Central Composite Design in Response Surface Methodology (CCD-RSM) and Sugeno method in Adaptive Network-based Fuzzy Inference System (ANFIS). As such, the adsorption isotherms including Temkin, Langmuir, Dubinin–Radushkevich (D-R) and Freundlich (two parameter equations), Sips, Toth and Khan (three parameter equations) were examined and interpreted. Finally, the adsorption kinetic models including Geometry, Boyd, Pseudo first and second orders, plus, Intra-particle kinetic models were studied thoroughly and discussed.