Control of the sulfide (S2-) concentration for optimal zinc removal by sulfide precipitation in a continuously stirred tank reactor

A.H.M. Veeken, L. Akoto, L.W.H. Pol, J. Weijma

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Abstract

Precipitation of Zn2+ with S2− was studied at room temperature in a continuously stirred tank reactor of 0.5 l to which solutions of ZnSO4 (800–5800 mg Zn2+/l) and Na2S were supplied. The pH was controlled at 6.5 and S2− concentration in the reactor was controlled at set point values ranging from 3.2x10−19 to 3.2x10−4 mg l−1, making use of an ion-selective S2− electrode
Precipitation of Zn2+ with S2- was studied at room temperature in a continuously stirred tank reactor of 0.51 to which solutions of ZnSO4 (800-5800 mg(-1) Zn2+) and Na2S were supplied. The pH was controlled at 6.5 and S2- concentration in the reactor was controlled at set point values ranging from 3.2 x 10(-19) to 3.2 x 10(-4) mg l(-1), making use of an ion-selective S2- electrode. In steady state, the mean particle size of the ZnS precipitate decreased linearly from 22 to 1 mum for S2- levels dropping from 3.2 x 10(-4) to 3.2 x 10(-18) mg l(-1). At 3.2 x 10(-11) Mg l(-1) of S2-, the supplies of ZnSO4 and Na2S solutions were stoichiometric for ZnS precipitation. At this S2- level, removal of dissolved zinc was optimal with effluent zinc concentration <0.03 mg l(-1) while ZnS particles formed with a mean geometric diameter of about 10 mum. Below 3.2 x 10(-11) mg l(-1) of S2- insufficient sulfide was added for complete zinc precipitation. At S2- levels higher than 3.2 x 10(-11) mg l(-1) the effluent zinc concentration increased due to the formation of soluble zinc sulfide complexes as confirmed by chemical equilibrium model calculations. (C) 2003 Elsevier Science Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)3709-3717
JournalWater Research
Volume37
Issue number15
DOIs
Publication statusPublished - 2003

Keywords

  • waste water treatment
  • zinc
  • removal
  • chemical precipitation
  • sulfides
  • sulfate reducing bacteria
  • sulfate-reducing bacteria
  • crystal precipitation
  • particle formation
  • sphalerite zns
  • solubility
  • mechanism

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