SOILS CONTAMINATED WITH HEXAVALENT CHROMIUM SORPTION MIGRATION AND

SOILS CONTAMINATED WITH HEXAVALENT CHROMIUM - SORPTION, MIGRATION AND REMEDIATION BRUNA FONSECA* Supervisor: Maria Teresa de Jesus Simões Campos Tavares University of Minho School of Engineering Cnetr of Biological Engineering * bfonseca@deb. uminho. pt How? Results (Highlights) Sampling Sorption and Migration Slightly acidic [p. H=5. 9] p. H 2 Poor in organic matter [3. 5%] Sorption and Migration The rate constant increases with the solution concentration Exists mainly as oxyanions Biobarrier Kaolinite [Cr(VI)] = 50 mg kg-1 Cr 2 O 72 - Carcinogenic Toxic Cr 2 O 72 - Cr. O 42 - HCr. O 42 - 76, 9 60 40 R = 77 % 20 7, 5 3, 7 4, 2 3, 2 2, 9 1, 6 100 80 80 60 44 45 40 Cr 2 O 72 - E = 10 V Cr 2 O 72 - Total Chromium USEPA 3051 Microwave acid digestion Flame Atomic Absorption Hexavalent Chromium USEPA 3060 A Alkaline digestion USEPA 7196 A Colorimetric method 44 17 20 e od th 5 0 de Electroremediation/Biobarriers Bacteria: Arthrobacter Viscosus (Cr 6+ → Cr 3+) Support: Activated carbon or Zeolite Hexavalent Chromium: Cr(VI) 80 Recovery = 100 % Ca Figure 3. Distribution of the Cr(VI) across the electrokinetic cell Cr(VI) oxyanions migrated towards the anode chamber. Rcarbon > Rzeolite 60 79 60 47 40 22 20 0 Zeolite Activated Carbon 9 Days Target Highly mobile 100 0 Analysis Figure 1. Overview of contaminants affecting soil and groundwater and the status of identification and clean-up of contaminated sites in Europe, as reported to the European Environment Agency through the EIONET priority data flows on contaminated sites. Langmuir equation Biobarriers no Sorption equilibrium Blank A Power function Electroremediation/Biobarriers (w//w 0)/% Sorption kinetics Freundlich equation Two-site non-equilibrium adsorption model The maximum sorption capacity decreases with p. H and concentration increasing R/% Flow tests Mathematical Modelling First order rate equation Figure 2. Variation of mass o Cr(VI) adsorbed per mass of soil, for different initial solutions, at p. H 2 and p. H 5, respectively (C 1=75 mg L-1; C 2=92 mg L-1; C 3= 128 mg L-1). 4 What about Europe? p. H 5 C/% Tested parameters • p. H of the contaminant solution; • Concentration of the contaminant solution. • Competition with other heavy metals in solution; Batch tests Best fit 3 U A C The soil was collected near an automobile repair shop, in a zone of great agricultural activity. Sorption kinetics: Single systems with Cr(VI) 2 S E S Main characteristics Bioacumulation of Heavy Metals Loamy sand soil 1 Why? 18 Days Zeolite Activated Carbon 9 Days 18 Days Figure 4. Fraction of Cr(VI) reduced to Cr(III) - C/% - and total removal of the Cr(VI) - R/%. In general… v. Conversion 18 d ≃ Conversion 9 d v. Removal 18 d > Removal 9 d For Activated Carbon… v. Conversion 18 d >Conversion 9 d v. Removal 18 d > Removal 9 d Acknowledgments The author gratefully acknowledge the Fundação para a Ciência e Tecnologia, Ministério da Ciência e Tecnologia, Portugal by her Ph. D grant (SFRH/BD/27780/2006). Uma Escola a Reinventar o Futuro – Semana da Escola de Engenharia - 24 a 27 de Outubro de 2011