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Graphical abstract Highlights • Chitosan-based flocculants with chelation and flocculation capacity are designed and prepared. • Relationship between flocculants structural and chelation-flocculation is investigated. • There is a certain linear relationship between heavy metal concentration and flocculants dosage. • Copper ions in mixed heavy metals solutions is preferentially chelated and flocculated. • The work provided valuable guidance in the design of eco-friendly polymeric flocculants. Abstract Dual-function chitosan-based flocculants with chelation and flocculation capacity, carboxylated chitosan-graft-polyacrylamide (PCA), carboxylated chitosan-graft-polyacrylamide-co-sodium xanthate (PCAXC), and carboxylated chitosan-graft-poly(acrylamide-2-acrylamido-2-methylpropane sulfonic acid) (PCAAF), are designed and prepared by UV initiation method. The physicochemical characteristics of PCA, PCAXC, and PCAAF were characterized by fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and X-ray diffraction pattern to confirm the successful syntheses. Then PCA, PCAXC, and PCAAF are applied to chelate and flocculate Cu, Cr, and Ni from water. Effects of pH, flocculants dosage, reaction time, and stirring speed were investigated systematically to detect the relationship between flocculants structural and chelation-flocculation capacity. The maximum removal rate of Cu and Cr obtained by PCAXC at are 85.1% and 76.1%, respectively, while The maximum removal rate of Ni obtained by PCAAF at is more than 75.7%%. In addition, the relationship between the initial concentration of simulated heavy metal wastewater and the flocculants dosage and the competitive chelation-flocculation properties in the mixed heavy metal solution are also detected in detail. The mechanism can be assigned to the effective interaction between function groups of the flocculants and heavy metal irons by chelation, charge neutralization, and adsorption bridging mechanism. [ABSTRACT FROM AUTHOR]

A novel chelating flocculant with branched architectures, polyacrylamide grafted maleoyl chitosan-mercaptoacetic acid (PAM-g-M(CS-MA)), was successfully fabricated using maleic anhydride as the "bridge" between chitosan and polyacrylamide. The functional groups and structural characteristic information of copolymers were obtained via characterization analysis. Flocculation performance was systematically investigated via purifying a series of simulated wastewater containing Cu or Cd. The properties of the flocs were studied to give in-depth evidences for the role of chelation groups and branched architectures in flocculation. Results indicated that PAM-g-M(CS-MA) showed excellent flocculation capacity for heavy metals in high concentrations and was superior to other chelating flocculants. The maximum flocculation efficiency of Cu (93.90%) and Cd (92.47%) was achieved by PAM-g-M(CS-MA) at pH 7, dosage of 100 mg L−1 and stirring speed of 90 rpm. The flocculation mechanisms of PAM-g-M(CS-MA) were deeply explored through the analyses of floc properties. The strong synergistic chelation of mercapto, carboxyl, amide and hydroxyl groups predominated for the capturing of heavy metals; and the branched architectures facilitated the formation of large and stable flocs via adsorption and bridging-furl effect. This study provided a solid foundation for the fabrication of flocculants for heavy metal wastewater treatment. [Display omitted] • A flocculant with branch architectures (PAM-g-M(CS-MA)) was synthesized. • PAM-g-M(CS-MA) showed low-dosage and efficient in heavy metals removal. • The maximum removal rates of Cu (93.90%) and Cd (92.47%) can be achieved by PAM-g-M(CS-MA). • Relationship between the branch architectures and flocculation performance was built. • Flocculation mechanism is composed by synergistic chelation, adsorption and bridging-furl effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high-efficiency, multifunctional, salt/pH-tolerant magnetic flocculant was successfully prepared. • The growth characteristics of flocs are systematically elucidated. • There is a positive correlation between the fractal dimension of flocs and flocculation efficiency. • Ca(II) and Fe(III) will promote the removal of DB56 and Cu(II), respectively. • The neural network models can accurately predict the removal rate of DB56 and Cu(II). In this study, an amphoteric magnetic chitosan (CS)-based flocculant MFe 3 O 4 @CS-g-PIA was prepared from CS, Fe 3 O 4 , and itaconic acid (IA), and its apparent morphology and characteristic structure were systematically studied. The flocculation performance and mechanism of the fabricated material were also investigated in different pollution systems, and the effects of total monomer concentration, m(CS):m(IA), IA pre-neutralization degree, reaction temperature, reaction time, and initiator concentration on the synthesis of MFe 3 O 4 @CS-g-PIA were studied. Characterization results showed that MFe 3 O 4 @CS-g-PIA forms a three-dimensional network with excellent magnetic induction. The optimal removal rates of Cu(II) and Disperse Blue 56 (DB56; 90.2% and 97.0%, respectively) were obtained under the conditions of 150 mg·L−1 MFe 3 O 4 @CS-g-PIA, pH 6.0, and 300 rpm stirring speed. MFe 3 O 4 @CS-g-PIA maintained removal rates of over 80.0% for Cu(II) and DB56 after five consecutive cycles of regeneration/flocculation and demonstrated excellent acid resistance stability. Changes in the particle size distribution, fractal dimensions, and zeta potentials of the flocs indicated that the relevant flocculation mechanism involves the synergistic functions of chelation, charge neutralization, and adsorption bridging. An artificial neural network model was finally established on the basis of the experimental flocculation data to predict the removal rates of Cu(II) (R = 0.97) and DB56 (R = 0.98) accurately. [ABSTRACT FROM AUTHOR]

• Novel functionalized chitosan flocculants are successfully synthesized. • Flocculation conditions for reaching high removal efficiencies are optimized. • Characterization results provided empirical evidence for existence of chelating groups. • "3E" triangular model was used to evaluate its flocculation-chelation properties. • Flocculation-chelation capacity profile indicated multiple potential applications. In order to effectively remove the dissolved heavy metals and the heavy metals on the colloidal particles during the flocculation process, a novel dual-functional chitosan flocculant CMCTS-g-P(AM-CA) is prepared by ultraviolet light-initiated graft polymerization using CMCTS, AM, and ammonium dithiocarbamate. The main influencing factors of monomer concentration, monomer ratio, pH value, photoinitiator concentration, and illumination time are investigated on the basis of intrinsic viscosity, grafting rate, and grafting efficiency of CMCTS-g-P(AM-CA). Characterization results provided empirical evidence for existence of chelating groups. In addition, CMCTS-g-P(AM-CA) was applied to treat the simulated heavy metals and electroplating wastewater. The effect of CMCTS-g-P(AM-CA) dosage, pH value, and reaction G value on flocculation efficiency was also explored. After the two-stage flocculation, the residual concentration of Ni(II), COD, and turbidity of actual electroplating wastewater decreased to 0.96 mg/L, 93.00 mg/L, and 1.71 NTU after flocculation tests at optimal condition, respectively. Finally, the "3E" triangular evaluation model is established and applied to evaluate the flocculation performance of CMCTS-g-P(AM-CA) on the actual heavy metal wastewater further, thereby proving its excellent chelation flocculation performance. [ABSTRACT FROM AUTHOR]

• Dual-functional flocculant with pH resistant is synthesized and used to remove heavy metals. • Flocculation conditions for reaching high removal efficiencies are optimized. • Optimal operation modulus was identified using 8 Key performance indicators by 3E triangle model. • Multi-objective programming optimization model was also established to evaluate Operation strategies. • Flocculation for heavy metal removal is superior in terms of engineering performance. Carboxymethyl chitosan (CMCTS) with active hydroxyl and amino groups is easily modified for chelating and capturing heavy metal, thus showing great potential for application in heavy metal-contaminated wastewater treatment. In this work, a dual-functional MACA copolymer [CMCTS-graft-P(AM-TGA)] with pH resistant was successfully designed and prepared by grafting acrylamide and thioglycolic acid onto CMCTS through UV-initiated graft polymerization. The spectroscopy characterization of functional groups and apparent morphology confirm the successful preparation of MACA. Flocculation conditions for reaching high removal efficiencies and investigating chelation capacity are optimized. A multiobjective evaluation model and a triangular environmental impact, economic benefit, and energy consumption (3E) evaluation model were established and employed to assess the 3E performance of MACA in heavy metal-contaminated wastewater flocculation. Optimal operation modulus is identified using 8 Key performance indicators by 3E triangle model. This work enriches knowledge about flocculation and provides guidance for flocculation parameter control. [ABSTRACT FROM AUTHOR]