Ions In Wastewater Research Articles

Constructing positively charged hollow fiber nanofiltration membranes with high performance for the treatment of wastewater containing heavy metal ions

The presence of heavy metal ions in wastewater has been identified as a significant environmental and human health concern. Positively charged hollow fiber (HF) Nanofiltration (NF) membranes show great promise and excellent potential for the removal of heavy metal ions due to Donnan exclusion effect. Nevertheless, the current limitations of positively charged HF NF membranes, including complex preparation process, low flux and poor selectivity, continue to impede their broader implementation. In this work, a high flux HF NF membrane with positively charged surface was fabricated via doping piperazine in the aqueous-phase solution of polyethyleneimine to modulate the interfacial polymerization and to adjust the structure of the subsequent polyamide skin layer. Subsequently, the surface of this nascent skin layer was modified with diethylenetriamine/ethanol solution to increase its positive charge density, and thus to improve the rejection of multivalent cations. The optimal HF NF membrane shows a pure water permeability of 160 LMH/MPa and a MgCl2 rejection of higher than 97 %. In addition, it shows a rejection of higher than 95 % for heavy metal salts such as CoCl2, MnCl2, NiCl2, CuCl2 and Cr2(SO4)3, and a rejection of more than 98 % for antibiotics such as tetracycline hydrochloride, oxytetracycline and levofloxacin. It also possesses good resistance to acid and contamination. In addition, the optimal HF NF membrane has been successfully scaled up to a module of 20 filaments and still shows excellent separation performance, suggesting its vast potential for industrial application.

Directed design of amorphous metal-organic frameworks for efficient and selective removal of Cu(II) from wastewater

Cu(II) is an essential trace element for the human body, but excessive concentrations in water or the human body can cause irreparable harm to ecosystems and human health. In this study, an amorphous metal-organic frameworks adsorbent (DKTA-MOF) was designed and synthesized using a hydrothermal method for the efficient and selective removal of Cu(II) from water. Various factors affecting the adsorption performance of DKTA-MOF were investigated, including solution pH, reaction time, initial concentration of Cu(II), temperature, coexisting ions, and the number of adsorption-desorption cycles. The experimental results indicate that the maximum adsorption capacity of DKTA-MOF is 160.5 mg/g at 318 K, and the optimal adsorption pH is 5. The adsorption process of Cu(II) by DKTA-MOF follows the pseudo-second-order (PSO) kinetic and the Langmuir isotherm models, indicating that the process mainly involves single-layer chemisorption. The adsorption process is spontaneous, driven by both electrostatic attraction and the sharing of lone pair electrons. DKTA-MOF demonstrates highly efficient and selective removal of Cu(II) in the presence of coexisting ions and maintains a high adsorption capacity after six cycles. Furthermore, the strategies and methods adopted in this design provide new perspectives for the removal of metal ions in wastewater.

Selective removal and monitoring of Pb(II) ions in wastewater using fluorescence-enhanced silicon quantum dot composites

In this study, we developed a novel composite film composed of silicon quantum dot (SiQD)-nanoSiO2-polyvinyl alcohol (PVA) (referred to as SSP). This composite film exhibits dual functionality for monitoring and removing heavy metal ions from wastewater. The composition and structure of the SSP composite film were confirmed through various techniques, such as via Fourier-transform infrared spectroscopy, thermogravimetry/differential scanning calorimetry, scanning electron microscopy SEM, and X-ray photoelectron spectroscopy. The evaluation of film adsorption performance revealed that the thermodynamic behavior of the adsorption process was consistent with the theoretical predictions of the Freundlich model. However, the adsorption kinetics were more accurately described by the Elovich model. At pH 6.0, SSP achieved a maximum adsorption capacity of 263.66 mg/g at 20 °C, as determined by the Langmuir model. Additionally, the adsorption of Pb(II) ions increased the fluorescence intensity of the composite material, enabling the monitoring of Pb(II) ion concentrations in wastewater. This composite film efficiently removed Pb(II) ions with high selectivity and sustained strong adsorption performance through five cycles, emphasizing its outstanding regeneration capability. Therefore, the proposed composite material exhibits significant potential for practical applications in wastewater treatment.

Functionalized Cyclodextrin/Carboxymethyl Cellulose Composite Hydrogel with Double Network Structure for Adsorption of Heavy Metal Ions in Wastewater.

Heavy metal ions in industrial wastewater pose significant environmental and ecological threats. In this work, a hydrogel featuring a double network structure was synthesized via radical polymerization and cross-linking of β-cyclodextrin (CD) and carboxymethylcellulose (CMC) with acrylic acid (AA). The hydrogel's functional groups and microstructure were characterized using Fourier transform infrared spectroscopy (FTIR-ATR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Mechanical properties were evaluated through rheological and compression tests. The study examined the impact of initial metal ion concentration, adsorbent-ion contact time, and solution pH on adsorption capacity. The maximum adsorption capacities of the functionalized CD/CMC-PAA-MBA hydrogel for Cu2+, Pb2+, and Cd2+ ions were 158.12, 393.56, and 290.12 mg/g, respectively. Notably, the hydrogel exhibited the highest selectivity for Pb2+ in mixed solutions. The adsorption kinetics of the metal ions were modeled using the pseudo-second-order rate equation and the Langmuir adsorption isotherm.

Fabrication of tight polyamide nanofiltration membrane by using a pyridine-diamine precursor for heavy metal ions removal

Nanofiltration offers a promising solution for removing heavy metal ions from wastewater, thereby mitigating ecological and environmental risks. In this study, we synthesized a novel pyridine-diamine precursor 2,6-dipiperazine pyridine (PyBPIP), and employed it as the sole aqueous monomer to fabricate tight polyamide (PA) nanofiltration (NF) membranes via interfacial polymerization (IP) method with trimesoyl chloride for the separation of heavy metals. The resulting membrane features an ultrathin PA functional layer (approximately 60 nm), a lower molecular weight cut-off of 251 Da, and a weakly negatively charged surface. This NF membrane exhibits competitive water permeance of approximately 7.67 LMH/bar and excellent rejection rates exceeding 98 % for various heavy metals ions including Zn2+, Mn2+, Cu2+, along with outstanding separation performance for other divalent cations. Additionally, the NF membrane also exhibits robust stability during the 72-h operational test. In summary, this study demonstrates the feasibility of designing suitable monomers for the preparation of highly perm-selective NF membranes for the removal of heavy metal ions in wastewater.

Increasing the stability and efficiency of an electrochemical ammonium separation system via state-of-charge (SoC) control

Ammonium ions in wastewater can induce toxicity in aquatic organisms and accelerate eutrophication. Therefore, the efficient removal of ammonium ions is necessary. The electrochemical ion separation method, based on an electrode with selectivity for ammonium ions, is a promising recovery technique that can efficiently adsorb and desorb ammonium ions. In this system, the electrode is composed of copper hexacyanoferrate (CuHCF) and silver (Ag), and ammonium ions are captured by the CuHCF electrode. However, the stability of the CuHCF electrode is not sufficient for continuous ammonium ion removal. We aim to report an improvement in the stability of this system realized through the use of the state-of-charge (SoC) control method. The stability of the system can be enhanced by using SoC control at only 60 % of the maximum capacity. After 300 cycles, the discharge capacity for the 60 % SoC approach remained at 55.8 %, showing a 10 % improvement in stability compared to the 100 % SoC method (45.8 %). Furthermore, in concentrated solutions with a ratio similar to that of domestic wastewater, the 60 % SoC control strategy exhibited ammonium removal capacity and selectivity comparable to that with 100 % SoC control but with higher energy efficiency (77 % reduction in energy consumption). These results indicate that the state-of-charge (SoC) control method can enhance both the stability and the efficiency of the electrochemical ammonium separation system.

Significant improvement in the removal performance of decimeter-sized zero-valent iron plates for mixed heavy metal ions in wastewater by enhancing surface sharpness

This study aims to lower the work function (Wa) of a decimeter-sized zero-valent iron plate (DZVIP) by introducing surface sharpness (TDZVIP) during stirring. Sharpness was achieved by cutting isosceles triangles with heights of 1 cm and varying apex angles (α) of 10˚, 20˚, 30˚, 40˚, and 50˚. A mixed simulated wastewater containing Cu(II), Te(IV), Se(IV), As(III), Bi(III), and Pb(II) at concentrations exceeding emission standards was prepared. Results indicate that the removal process exhibits mixed kinetic behavior, and sharpness significantly enhances the removal capacity (Re), mean removal rate (Vm), recycling performance, and final discharge quality. The Vm values for Cu(II), Te(IV), Se(IV), As(III), Bi(III), and Pb(II) over TDZVIP with optimized α are 2.34, 1.97, 1.51, 1.59, 4.09, and 1.53 times higher, respectively, than those over PDZVIP (without sharpness). UPS measurements provide direct evidence of Wa reduction, while XRD offers indirect confirmation. This is the first time the Wa of the amorphous shell has been identified and verified as a critical potential barrier for core electrons transferring from the DZVIP surface to wastewater. Additionally, it has been successfully reduced by incorporating surface sharpness and stirring, leading to enhanced removal efficiency, improved recycling performance, and higher final discharge quality.

Ethylene Glycol (EG)-Derived Chlorine-Resistant Cu0/TiO2-x for Efficient Photocatalytic Degradation of Nitrate to N2 without Sacrificial Agents at Near-Neutral pH Conditions: The Synergistic Effects of Cu0 and EG Radicals.

The selective photoreduction of nitrate to nontoxic nitrogen gas has emerged as an energy-efficient and environmentally friendly route for nitrate removal. However, the coexisting high-concentration chloride ions in wastewater can exert a significant influence on nitrate reduction due to the competitive adsorption and corrosion of Cl- on photocatalysts. Herein, we prepared ethylene glycol-Cu/TiO2-x (EG-Cu/TiO2-x) through a solvothermal reaction of Cu-doped TiO2 in an EG solution. The photodegradation of nitrate using EG-Cu/TiO2-x without adding sacrificial agents can efficiently occur in near-neutral pH solutions containing 50 mM Cl- with 95.26% of NO3- removal and 76.52% of N2 selectivity. Moreover, the photocatalyst performance remained at a high level after 8 cycles. In this work, NO3- was first converted to NH4+ by Cu0 and Ti3+, followed by the NH4+-to-N2 conversion by photogenerated chlorine free radicals. Compared to HO•, Cl•, and Cl2•-, ClO• is proved to play the predominant role in transforming NH4+ to N2. The EG radicals produced by UV light impede Cl- adsorption on Cu, protecting Cu0 from being corroded. What's more, photoelectrons can reduce Ti4+ to Ti3+ and protect Cu0 from being oxidized, enabling the stability of reactive sites. This work provides novel insights and understanding on designing photocatalysts for NO3- removal in solutions containing chloride ions, highlighting the significance of eliminating Cl- by EG radicals and adjusting the conversion process of NO3- for the efficient removal of NO3-.

Complexation mechanism and adsorption modes of Cu (II) ions by wool keratin powder

The excessive presence of Cu (II) ions in wastewater has led to various health problems. Using wool keratin powder adsorbent, the adsorption of Cu (II) ions in wastewater was explored. The adsorption mechanism and efficiency of keratin powder towards Cu (II) ions were characterized by infrared spectroscopy, x-ray diffraction and scanning electron microscopy. The results indicate that the particle size of keratin powder has a significant impact on its adsorption performances. Keratin powder with smaller particle size has more adsorption sites, larger specific surface area, higher porosity and more effective adsorption capacity. After adsorption of Cu (II), the average diameter of keratin powder increased by 11.48 μm. The adsorption capacity reached 58.95 mg g−1, and the adsorption efficiency reached 99.52% after 12 h of contact time. The research results not only provide an effective solution for Cu (II) ion pollution in wastewater, but also explore the resource utilization of waste wool.

CTAB-Si Nanoparticles Derived from Rice Husk Ash for Nitrate Ions Removal in Simulated Wastewater

In this study, silica (Si) nanoparticles derived from rice husk ash is coated with cetyltrimethylammonium bromide (CTAB), a cationic surfactant, and used as adsorbent of nitrate ion in wastewater. CTAB functionalized Si (CTAB-Si) nanoparticles were characterized using scanning electron microscope (SEM), energy dispersive X-Ray (EDX), dynamic light scattering (DLS) Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The synthesized CTAB-Si nanoparticles has a non-spherical shape, with visible polydispersity and is amorphous with average particle size of 72nm. It showed stretching vibrations of silanol at 963cm-1, siloxane at 1073cm-1, sharp peaks at 2852cm-1 and 2922cm-1 due to the methylene tail of CTAB and amine peak at 1,384cm-1. An ∼80% nitrate removal and adsorption capacity of 7.98 mg NO3/g CTAB-Si nanoparticles was obtained at optimized condition using Face Centered Central Composite Design (FC-CCD) at pH 4, 50 mgL-1 of adsorbate concentration, 0.2 gL-1 adsorbent dose and 30 minutes contact time. The adsorption isotherm and kinetic models fits well in Langmuir model and Pseudo second order with a R2 of 0.984 and 0.999 respectively. The efficiency of the nanoparticle after 5 adsorption cycles was ∼50% nitrate removal.

Harnessing biomass derived carbon material with heteroatoms for sensitive and selective detection of mercury (II) ions in waste water

A wide range of raw materials can be converted into carbon materialsprimarily through chemical and physical activation, or a combination of both. The characteristics of resultant carbon material depend significantly on activation method and the specific raw materials used. This work processes date seed biomass using a chemical activation and thermal annealing method to derive a low-cost and porous carbon material DS-AC@400. The material was then used as a fluorescent sensing probe for selective and precise detection of Hg2+ ions in wastewater. There was a linear correlation between Hg2+ concentration and fluorescence intensity of DS-AC@400 with a limit of detection of 8.69 nM. It was found that the DS-AC@400-based fluorescent sensor has a high selectivity for Hg2+ detection against other interferingmetal ions. The sensor workedeffectively in real water samplesfor practical applications with little interference from interfering ions.

Fabrication of a polyoxometalate-based metal-organic compound and its derivative for enhanced photocatalytic, electrocatalytic, and electrochemical sensing properties

A novel polyoxometalate-based metal-organic compound (POMOC), namely [Ag(3-pna)2(H2PW12O40)]n (compound 1, where 3-pna = N-(pyridine-3-yl)nicotinamide), had been successfully synthesized and structurally characterized. The photocatalytic performance of compound 1 for the degradation of gentian violet (GV) and methylene blue (MB) was investigated in detail, which exhibited good cyclic stability as a photocatalyst. In addition, cyclic voltammetry technology was used to verify that compound 1 exhibited excellent electrocatalytic performance towards KBrO3 and H2O2. To improve the degradation of organic dyes and electrochemical sensing performance, a negatively charged oxygen vacancy metal oxide compound 1@C was prepared via pyrolysis using compound 1 as a precursor. Compound 1@C was investigated as an adsorbent, and was found to effectively remove MB and GV from wastewater, with adsorption rates of 824.36 mg/g and 957.02 mg/g, respectively. The performance of compound 1@C/glassy carbon electrode as an electrochemical sensor was studied using differential pulse dissolution voltammetry (DPV). This method proved effective in detecting heavy metal ions Cd2+ and Pb2+ in wastewater with the limits of detection as 4.65 and 1.69 μg/L, respectively. Compound 1@C/GCE showed good anti-interference capabilities and stability in detecting heavy metal ions in wastewater.

A novel technique of dual modified acid-washed layered double hydroxides-biochar for adsorption and as potential catalysts for electrochemical applications

The enhanced concentration of nitrate ions in wastewater delivered from industries has led to consequential environmental issues and severe health problems for humanity. Considering the advantages to the environment and being cost-effective, adsorption techniques based on biochar materials have appeared as a remarkable strategy to adsorb nitrate. Although the porous nature of the biochar materials aids in adsorption, the stability is a significant hindrance, thus limiting nitrate adsorption. Thus, in an effort to tackle this difficulty, layered double hydroxide (LDH) modified with cationic surfactant rice husk biochar is utilized to enhance the stability and the performance of nitrate adsorption. In the current research, pristine biochar (Pure-BC), surfactant-modified biochar (BC-S), varying concentrations of iron and magnesium-modified LDH with surfactant biochar materials (FM-SL, MF-SL) were synthesized, and batch experiments were conducted in order to explore their performance of nitrate adsorption. The acid-washed biochar exhibited novel rapid adsorption within a period of 10 min and a maximum adsorption capacity of 72 mg/g at neutral pH, whose mechanism was based on both physical and chemical adsorption. Further, the pristine and modified biochar materials were analyzed for their electrochemical behavior in order to explore their chemical reactivity and electron transfer kinetics, with an overpotential value of 67 mV. Thus, the prepared biochar materials, being inexpensive, exhibit potential adsorbents for the adsorption of nitrate from industrial sewage waters and display better electrochemical characteristics.

Highly selective removal of thallous ions from wastewater using Prussian Blue biochar composite

Thallium, a highly toxic pollutant, shows greater toxicity to human than other common heavy metals such as mercury, lead, cadmium and its effective removal from wastewater gains great attention. The main restriction for the Tl+ removal is the interference of a high concentration of co-existing ions in wastewater. Therefore, the goal of the current work was to synthesis adsorbent with high selectivity for the Tl+ removal. Herein, the pore size sieving strategy was proposed and Prussian blue-impregnated biochar (BC@PB) particles was synthesized. More than 95% Tl+ can be removed even the concentrations of the coexistence ions (Na+, Cd2+, and Zn2+) 1,000 higher than the initial concentration of Tl+ (500 μg/L). BC@PB also showed large adsorption capacity (9365 μg/g) and more than 99% Tl+ (initial concentration, 500 μg/L) were removed in just 1 min. The BC@PB had excellent and stable Tl+ removal ability (> 99%) over a range of pH from 3 to 9, which covered the pH range of common thallium-containing wastewater. The density functional theory (DFT) calculation confirmed that not only hydrated volume but also the hydration free energy of ions, which governed the energy barrier for ions entering into narrow channels of BC@PB, played essential roles on the selectivity removal of Tl+. Overall, due to its high selectivity, high adsorption capacity and easy preparation process, the synthesized BC@PB particles based on the pore sizing sieving strategy, can be a promising candidate for the removal of thallium from wastewater.

Construction of controlled hyper-crosslinked nanofibrous tubes for Cr(VI) removal: Response surface, kinetics, and isotherm

Porous organic polymers (POPs) exhibit significant potential for adsorbing toxic metal ions in wastewater. Developing POPs with controlled morphologies is a pivotal direction in this field. This study synthesized a series of novel hyper-crosslinked nanofibrous tubes designated HCNT-Cn (n = 4, 8, 12, 16) via Friedel-Crafts alkylation and quaternization reactions. These reactions were fine-tuned through a post-synthetic strategy involving varying alkyl chain lengths. These materials were characterized using FT-IR, SEM, N₂ adsorption-desorption isotherms, among others, and they were specifically evaluated for their ability to adsorb Cr(VI). Among the variants, HCNT-C₄ exhibited the highest specific surface area (495.26 m2 g−1), superior hydrophilicity (CA = 48.7°), and optimal adsorption performance. The adsorption kinetics of HCNT-C₄ conformed to a pseudo-second-order model, while its adsorption isotherm aligned with the Langmuir model. An investigation into the impact of Cr(VI) removal was conducted using three independent variables in a Central Composite Design (CCD) response surface model, revealing that under optimal conditions, the Cr(VI) removal efficiency reached 98%. Additionally, a mechanism for Cr(VI) adsorption on HCNT-C₄ was proposed. It was also found that HCNT-C₄ could be reused up to four times, maintaining a removal efficiency of 70%. This study suggests potential applications for removing Cr(VI) from contaminated wastewater.

Selective adsorption of gold ion in wastewater with competing cations by novel thiourea-reduced graphene oxide

In this study, selective adsorption experiments of Au were carried out using graphene oxide (GO) and thiourea-reduced GO (TU-rGO). Adsorption experiments using Au, Cu, Pb, and Zn were performed with GO and TU-rGO in order to selectively adsorb Au from simulated waste electric and electronic equipment leachate or printed circuit board wastewater. Optimal adsorption conditions were determined, adsorption isotherm models were fitted, and desorption and regeneration experiments were performed. Additionally, GO and TU-rGO were characterized to better understand the material and propose the adsorption and desorption mechanisms for TU-rGO. It was found that TU-rGO could selectively adsorb Au, achieving a high efficiency of 95‒99% at initial Au concentrations of 0.1‒10 mg L−1 with little to no adsorption of Cu, Pb, and Zn. Moreover, the desorption efficiency of Au by ammonium thiosulfate reached 94% with the adsorption efficiency of TU-rGO decreasing from 99 to 78% after five adsorption and desorption cycles. Isotherm adsorption experiments indicated that the Langmuir model better fitted the adsorption of Au than the Freundlich model. This implied that the adsorption process was mainly controlled by monolayer coverage, with a high Au adsorption capacity of approximately 833 mg g−1 for TU-rGO.

Facile synthesis of poly(tannic acid-1,4-butanediamine) microsphere based on the “self-assembly to polymerization” mechanism and its fast removal feature toward Cr(VI) ions

To remediate toxic Cr(VI) ions in wastewater is a daunting environmental challenge nowadays, thus advanced adsorbents are developed and used to overcome the low removal rate of existing technologies. Herein, poly(tannic acid-1,4-butanediamine) (PTBA) microspheres were synthesized for the purpose of fast removal of Cr(VI) from the aqueous phase. The synthesis was based on the “self-assembly to polymerization” mechanism. The microstructures and chemical characteristics of the fresh and used adsorbents PTBA were characterized systematically by means of TEM, SEM, FT-IR, XPS, TGA and XRD. Effects of pH, contact time, Cr(VI) initial concentration, PTBA dosage, temperature, and the presence of foreign ions on the removal of Cr(VI) had been investigated sequentially. The results indicated that almost 100% of removal efficiency could be achieved in short time intervals, based on the initial concentration of Cr(VI). The spontaneous and endothermic adsorption behavior could be well described by the pseudo-2nd-order (P2O) and Langmuir isotherm models. Finally, the process of partial reduction of Cr(VI) to non-toxic Cr(III) during the adsorption process was explained. Overall, the refined PTBA adsorbent presents a satisfactory behavior to ameliorate the Cr(VI)-pollution elimination means.

The Review of Treatment of Copper Ion in Wastewater and Comparison Between Four Treatment

This paper presents a comprehensive review of various methods used to remove copper ions from wastewater, highlighting their efficiency and feasibility. The main focus is on adsorption, ion flotation, membrane-based techniques, and electrochemical cells, with a particular emphasis on innovative approaches like the use of graphene oxide electrodes. The comparison and analysis section assesses each method’s removal efficiency, operational challenges, and costs, providing a critical perspective on their practical application in industrial settings.

Characterization and Adsorption Capacity Evaluation of ZnCl2 Impregnated Cassava Peel Carbon for Removal of Fe, Ca, Mg and Zn ions in Wastewater from Cassava processing Industry

The objective of this paper was to prepare, characterize and evaluate the adsorption capacity of cassava peel carbon (CPC) impregnation with ZnCl2 salt for the removal of Fe, Ca, Mg and Zn ions in wastewater derived from cassava processing which has been noted to be problematic in terms of management. CPC and cassava peel activated carbon (CPAC) at 1:3, 2:3, and 1:1 impregnation levels were placed in fixed bed adsorption columns to determine metal ion adsorption capacities of the carbon materials after 120, 240, 360 and 480-minute contact times. Langmuir and Freundlich isotherm models were used in assessment of adsorption of the carbon materials, while pseudo-first and second order models were used to validate the adsorption kinetics of Fe, Ca, Mg and Zn. Pore space development was also monitored using scanning electron microscope (SEM) imagery. Results SEM images revealed hexagonal honeycomb surface structure at 2:3 impregnation level and spongy configuration at 1:1 ZnCl2 impregnation level. The correlation coefficient of Langmuir isotherm was observed to be between 0.86 to 1, indicating that the adsorbent is very good in adsorption of the metals, however, Freundlich isotherm is found to be unfavorable in describing CPAC’s capacity in adsorbing zinc ion contaminant. The pH of the carbon materials was observed to have increased while the bulk density reduced with increasing level of impregnation. Conclusively, CPC and CPAC materials are well suited to Langmuir isotherm as well as pseudo-second order model, implying that adsorption occurs well in a monolayer form on the surface material surface.

Study on the preparation of Nano-Fe3O4 by steel pickling waste liquor and its effective removal of Cr (VI) from wastewater

In order to comprehensively treat and utilize steel pickling waste liquor (SPWL), this study used SPWL as raw material to prepare two different crystalline forms of Nano-Fe3O4 by co-precipitation and precipitation-oxidation methods, and investigated their removal effect on Cr(VI) in wastewater. The two kinds of Nano-Fe3O4 were characterized using SEM, XRD, and VSM, and the results showed that the Nano-Fe3O4 synthesized by the co-precipitation method has better properties. The two kinds of Nano-Fe3O4 were used to remove Cr(VI) in wastewater, the adsorption capacity could reach 38.38 mg/g and 15.83 mg/g, respectively. Five adsorption kinetic models and five isothermal adsorption models were used to study the adsorption mechanism of Fe3O4 on Cr(VI). The adsorption process of Cr(VI) by Nano-Fe3O4 was explained well using the pseudo-second-order and Freundlich isotherm model, and the results showed that the adsorption process mainly involved physical and chemical adsorption. Through the characterization analysis before and after the reaction, the removal mechanism of Cr(VI) by Nano-Fe3O4 prepared from SPWL is mainly attributed to electrostatic adsorption and reduction reaction. According to the market survey and analysis, the production cost is reduced by at least 58.33 % compared to that of Nano-Fe3O4 prepared using analytical purity in the market. Therefore, the preparation of Nano-Fe3O4 by steel pickling waste liquor provides an economical and effective way to remove heavy metal ions in wastewater.