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The sequence with regard to complexing abilities of Carboxyl methyl cellulose is Cu> > Cd2+> Cog+> Zn2+> Ni2+.These results show that the affinity found from CMC towards Cu2+ is suited to the Irving-Williams series, but zinc complexation is surprisingly low

Removal and recovery of copper from wastewater by a complexation-ultrafiltration process

Desalination, no. 1-3 (2004): 201-209

Cited by: 43|Views3
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Abstract

Carboxyl methyl cellulose (CMC) as a water-soluble metal-binding polymer in combination with ultrafiltration (UF) was used in a hybrid approach for selective removal and recovery of copper from water. In the complexation-UF process the cationic forms of heavy metals were first complexed by a macro ligand in order to increase their molecul...More

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Introduction
  • Among the various processes used for heavy metal removal from water, the technique of complexation-ultrafiltration proved to be a promising alternative to technologies based on precipitation and ion exchange.
  • The single metal ion experiment, both in low and high ion-strength conditions, was performed at the optimal Me:CMC ratio of 1:6 and pH 8.
  • The behavior of permeate flux decay was similar for all single metal ions studied, both at low and high ion-strength conditions.
Highlights
  • Among the various processes used for heavy metal removal from water, the technique of complexation-ultrafiltration proved to be a promising alternative to technologies based on precipitation and ion exchange
  • In the complexationUF process cationic forms of heavy metals are first complexed by a maeroligand in order to increase their molecular weight with a size larger than the pores of the selected membrane that can be retained and which flow out in the retentate; permeate water is purified from the heavy metals
  • The sequence with regard to complexing abilities of Carboxyl methyl cellulose (CMC) is Cu> > Cd2+> Cog+> Zn2+> Ni2+.These results show that the affinity found from CMC towards Cu2+ is suited to the Irving-Williams series [6], but zinc complexation is surprisingly low
  • A comparison of the results of metal separation obtained at the same pH and at different ion strengths of the solutions treated indicated that the decomplexation effect appears to be independent of ion strength (Table 2)
  • As the current study focused to a certain extent on solving the specific problem of copper recovery from copper-rich effluents, experiments with synthetic water containing copper as the sole heavy metal were performed
Results
  • The retention observed for Pb and Cu was much higher than the corresponding values for Ni and Zn. The order of metal rejection was Cu > Pb > Ni >Zn. According to the Irving-Williams series [6], which ranks the divalent metal ions in their tendency to complexity, regardless of the nature ofthe eomplexing agent, the cations were ranked as follows: CuZ+>Zn>>Pb2+>Ni2+.Current results confirm the previous data [5], which indicated a low complexation ability of CMC towards zinc.
  • A comparison of the results of metal separation obtained at the same pH and at different ion strengths of the solutions treated indicated that the decomplexation effect appears to be independent of ion strength (Table 2).
  • No differences of permeate flux registered through the UF2 step for both the low and high strength experiments were found.
  • Regarding the values of copper retention through the first separation step, the results are acceptable with a certain advantage at higher CMC:Cu ratios.
  • Attempts to perform the second step of separation, following the pH adjustment of the UF-1 retentate obtained at the Cu:CMC ratio of 1:6 failed because o f the very low permeate flux registered.
  • The metal separation (UF-2 step) that followed the pH decrease was quite high; the copper retention was below 3%, i.e., over 97% of the copper was transferred into the permeate.
  • An obvious transient flux decay was registered through the UF-1 step of treatment (Fig. 4) for both Cu-CMC ratios studied.
Conclusion
  • The results show as well that in the treatment of highly polluted water with heavy metals, the transient permeate flux dropped significantly, both during the UF-1 and UF-2 step.
  • Regarding the transient permeate flux during the membrane separation of complexes, some of the data obtained indicate that, while at low heavy metal concentration, the optimal metal: CMC mole ratio is 1:6; at higher metal concentrations, a lower mole ratio, 1:2 or 1:1, is preferable.
  • ° Several experimental results show that the rejection of metal-CMC complexes is improved in treatment of drainage mine water compared to synthetic water with the same heavy metal concentration.
Summary
  • Among the various processes used for heavy metal removal from water, the technique of complexation-ultrafiltration proved to be a promising alternative to technologies based on precipitation and ion exchange.
  • The single metal ion experiment, both in low and high ion-strength conditions, was performed at the optimal Me:CMC ratio of 1:6 and pH 8.
  • The behavior of permeate flux decay was similar for all single metal ions studied, both at low and high ion-strength conditions.
  • The retention observed for Pb and Cu was much higher than the corresponding values for Ni and Zn. The order of metal rejection was Cu > Pb > Ni >Zn. According to the Irving-Williams series [6], which ranks the divalent metal ions in their tendency to complexity, regardless of the nature ofthe eomplexing agent, the cations were ranked as follows: CuZ+>Zn>>Pb2+>Ni2+.Current results confirm the previous data [5], which indicated a low complexation ability of CMC towards zinc.
  • A comparison of the results of metal separation obtained at the same pH and at different ion strengths of the solutions treated indicated that the decomplexation effect appears to be independent of ion strength (Table 2).
  • No differences of permeate flux registered through the UF2 step for both the low and high strength experiments were found.
  • Regarding the values of copper retention through the first separation step, the results are acceptable with a certain advantage at higher CMC:Cu ratios.
  • Attempts to perform the second step of separation, following the pH adjustment of the UF-1 retentate obtained at the Cu:CMC ratio of 1:6 failed because o f the very low permeate flux registered.
  • The metal separation (UF-2 step) that followed the pH decrease was quite high; the copper retention was below 3%, i.e., over 97% of the copper was transferred into the permeate.
  • An obvious transient flux decay was registered through the UF-1 step of treatment (Fig. 4) for both Cu-CMC ratios studied.
  • The results show as well that in the treatment of highly polluted water with heavy metals, the transient permeate flux dropped significantly, both during the UF-1 and UF-2 step.
  • Regarding the transient permeate flux during the membrane separation of complexes, some of the data obtained indicate that, while at low heavy metal concentration, the optimal metal: CMC mole ratio is 1:6; at higher metal concentrations, a lower mole ratio, 1:2 or 1:1, is preferable.
  • ° Several experimental results show that the rejection of metal-CMC complexes is improved in treatment of drainage mine water compared to synthetic water with the same heavy metal concentration.
Tables
  • Table1: Retention (Rur_t) at the different stages of membrane separation a
  • Table2: Retention (RuF.2) following pH decrease of retentate
  • Table3: UF-1 retention at different Cu:CMC ratio
  • Table4: UF-2 retention at different Cu:CMC ratio
  • Table5: Results obtained from mine drainage water
Download tables as Excel
Funding
  • The destruction of complexes of heavy metals from the real wastewater was limited - - up to 80%
  • The metal separation (UF-2 step) that followed the pH decrease was quite high; the copper retention was below 3%, i.e., over 97% of the copper was transferred into the permeate
  • In the case of real wastewater treatment, copper retention was over 99%
Study subjects and analysis
cases: 3
The results obtained show that a low mole Cu:CMC ratio favors both ultrafiltrate permeability during the first stage of the process and the separation following the next step of complex destruction at a lower pH. The comparativeexperiments with (1)synthetic water containing copper as a single heavy metal; (2)copper containing a solution with addition of ferrous iron, manganese and lead; and (3) drainage mine water contaminated with copper, ferrous iron, manganese and lead show a selectivity for Cu during the first stage of UF approaching 99% in these three cases. However, the destruction of complexes of heavy metals from the real wastewater was limited - - up to 80%

Reference
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