| Spent pickling solutions are strongly acidic and contain multiple typical heavy metal ions(Cu,Ni,Co,etc.)and high concentration of ferrous ions,their total emission are large and the risk are high.Conventional handling methods are facing some difficulties and challenges,such as large consumption of medicine,large amount of hazardous wastes,secondary pollution,resource waste and so on.Moreover,poorly resistant to acid,low adsorption capacities and selectivity in high-acidity solutions are disadvantages of most separating materials.Therefore,it is of great significance to develop novel adsorbents and techniques to selectively remove and exclusively recover heavy metal ions from high-acidity solutions.Pyridine chelating resins have unique advantages of acid resisitance and high selectivity.In this work,amine and pyridine were successfully grafted onto polymethacrylate-divinylbenzene matrix by two steps,getting the novel acid-resistant chelating resins(PABPY).Characterization involving Elemental Analysis(EA),Scanning Electron Microscopy(SEM),Pore Size Distribution(PSD),Fourier Transform Infrared Spectroscopy(FTIR)and X-ray photoelectron Spectrometry(XPS)were illuminated qualitatively and quantitatively for contents of functional groups and physicochemical structure.The adsorption and separation behaviors towards heavy metal ions onto PABPY were systematically explored by carrying out the sole-/binary-/multiple-component static and dynamic experiments under the condition of high acidity with or without high-concentration ferrous ions.The mechanisms of selective separation and removal of heavy metal ions could be revealed.The integrated technique for multi-step controlling and recovering heavy metal ions from spent pickling wastewater would be developed.In high-acidity systems without ferrous ions,as pH values rised,the adsorption capacities of PABPY toward Cu(?),Ni(?),Co(?)and Fe(?)first increased and then tended to flat,and the adsorption capacities followed the order of Cu(?)>Ni(?)>Co(?)>Fe(?)at the same pH value.It is determined that pH values of 1,2 and 2.5 were the optimum points to selectively separate Cu(?)/Ni(?),Ni(?)/Co(?),Co(?)/Fe(?),respectively.The adsorption isotherms could be well fitted by Langmuir model with the maximum adsorption capacities of 1.538 mmol/g,1.484 mmol/g and 0.927 mmol/g for Cu(?),Ni(?)and Co(?)on PABPY at.the optimum pH values and 298 K,respectively.The maximum adsorption capacities for Cu(?)and Ni(?)on PABPY were 4.48%?6.73%and 7.07%?16.94%higher than those on commercial pyridine chelating resins M4195 and TP220,respectively.While the maximum adsorption capacity for Co(?)on PABPY was 34.74%higher than that on M4195 and 5.79%lower than that on TP220.The adsorption processes were endothermic,spontaneous and impelled by entropy through the thermodynamic analysis.The kinetic data could be well fitted by pseudo-second-order model.In binary adsorption kinetics of Cu(?)/Ni(?)and Ni(?)/Co(?),compared with sole Cu(?)or Ni(?)system,the adsorption capacities of Cu(?)and Ni(?)by PABPY decreased by 3.86%and 1.91%,while those by M4195 and TP220 declined by 5.08%?8.37%and 2.43%?16.57%,respectively.The separation factors for three resins between Cu(?)and Ni(?)or Ni(?)and Co(?)were all increased as the initial molarity ratio increased from 1:1 to 1:500,with the order of PABPY>M4195>TP220,and those for PABPY were 33.67%?155.79%or 105.38%?725.00%higher than those for TP220.In binary dynamic adsorption,Ni(?)could be replaced by Cu(?)obviously,similarly,Co(?)could be replaced by Ni(?)with ease.Moreover,PABPY could obtain the purity of nickel or cobalt up to 99.9%in the former 110 BV or 65 BV,respectively.PABPY exhausted by Cu(?)or Ni(?)or Co(?)was regenerated using 20%or 10%or 10%HCl solution as the preferential eluting agent.Continuous 5-cycle adsorption-regeneration circulations of the identical PABPY column were performed to testify good regeneration and reusability of PABPY.The adsorption mechanism was demonstrated by the analysis of FTIR,XPS spectra and the calculation of Density Functional Theory(DFT),indicating that heavy metal ions could coordinated with the nitrogen atoms from amine group and two pyridyl groups to form two five-member rings structure.Furthermore,affirmed by Energy Dispersive X-ray Spectroscopy(EDS),XPS and preloading tests,inferior components on solid phase could be completely replaced by preponderant ones,and the different deprotonation of heavy metal ions were revealed as the leading mechanism for selective separation.Different concentrations of ferrous ions had little effect on the adsorption capacities of PABPY for Cu(?),Ni(?)and Co(?).In high-acidity systems with high-concentration ferrous ions,the kinetic data also were well fitted by pseudo-second-order model,and the initial adsorption rates of single heavy metal ions were hardly affected by high-concentration ferrous ions.The adsorption isothermal surface could be well fitted by Extended Langmuir model,showing the affinities followed the order of Cu(?)>Ni(?)>Co(?)and the coexistence of high-concentration ferrous ions had little effects on separation of heavy metal ions by PABPY.Under the condition of high-concentration ferrous ions,the adsorption kinetics of preponderant components were basically consistent with those at non-ferrous solutions and the rates of replacing inferior components with preponderant ones could be improved.It was speculated that the inferior components approaching to resins was obstructed by high-concentration ferrous ions.In high-acidity systems and high-concentration ferrous systems,reducing the flow rates of dynamic column could significantly enhance the separation efficiencies of heavy metal ions by PABPY,with the breakthrough points of preponderant components moving backward and the saturation point moving forward.2.5 BV/h was the preferred flow rate and the purity of nickel or cobalt or ferrous up to 99.0%was obtained by PABPY in the former 200 BV or 135 BV or 80 BV in 2.5 BV/h,which was 14.28%?42.86%and 33.33%?125.00%higher than those in 5 BV/h and in 10 BV/h,respectively.According to the theoretical research mentioned above,an integrated technique to multi-step control,selectively remove and exclusively recover typical heavy metal ions from spent pickling watewater was proposed with PABPY resin.With the same separating effect(purity of effluent>99.0%),it was the most economical to choose the flow rate of 5 BV/h and the total cost for 5 BV/h was 32.43 yuan/t/d,which was 12.66%and 5.18%lower than that for 2.5 BV/h and 10 BV/h,respectively.Besides,the income of recovering heavy metals was up to 48.08 yuan/t/d in 5 BV/h.Conclusively,this work could provide a new material and method to remove and to recover typical heavy metal ions from spent pickling wastewater. |
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