Presentation Overview

1. Recovery of metals from waste sludge/filter cakeProject QUB18/08/11 Charles Campalani Dr G. Walker, Dr. A.P. Doherty and Prof. S. AllenSchool of Chemistry and Chemical EngineeringQueen’s University Belfast

2. Presentation Overview Introduction Objectives Results Summary Future work 2

3. Introduction • The electroplating industries can produce large volumes of wastewaters which contain high concentrations of metal pollutants. • Heavy metals are of particular interest, specifically: chromium, copper and aluminium. • These metals are mainly concentrated through the wastewater treatment and filtration processes producing filter sludge cakes with high metal concentration.

4. 3 Project Objectives • To investigate the potential of recovering metallic chromium from filter sludge produced by Bombardier. • To determine the feasibility of electro-deposition process for chromium: • Via acid dissolution of filter cake • Chromic acid formation • Electrolysis using carbon/copper electrodes • To find the optimum conditions for chromium adsorption and separation of heavy metals in single, binary and ternary solutions. • To develop a process for removal/concentration of Cr(III) under flow conditions (pilot plant).

5. Results – Initial dissolution • Successful acid/base dissolution • 1.0 molar sulphuric acid gave highest Cr conc. • Equilibrium achieved < 60 seconds

6. Results – electro-deposition • Initial electro-deposition of Chromium using carbon/copper electrodes proved problematic • Possibly due to: concentration? impurities?

7. Results – analysis of filter-cake ICP analysis of the Bombardier sludge cake indicated the complexity of the impurities in the filter sludge, therefore, current work focussing on developing an adsorption process to purify and concentrate chromium prior to electro-deposition. Cr 17% w/w in sludge, < 5% in acidic solution.

8. Why adsorption? • There are several methods considered for the purification of the filter sludge cake, such as ion exchange, ultra-filtration, membrane technologies, chemical reaction and adsorption columns. • The reason that adsorption method was chosen over the other methods suggested above is mainly due to cost implications and the degree of difficulty obtaining results. • As ion exchange are expensive, the ultrafiltration and the membranes become clogged up and are expensive to replace.

9. Adsorption studies • The removal of the Chromium were undertaken using granular activated carbon (GAC). • Aim is to develop a multi-component adsorption model to predict Cr uptake in a complex system. • IAS theory model • Process parameters include: pH, initial concentration of chromium in aqueous solution, the effect of the addition of Cu, Al, Fe(II), Fe(III) and selenium to aqueous chromium.

10. Adsorbent - Activated Carbon • GAC has a high utilization capacity. Can be employed in counter current flow mode which results in multistage equilibrium and resultant higher specific removal rates. • GAC can be reactivated economically by thermal processing. • GAC treatment ensures continuous vigilance in the removal of a great number of toxic and other undesirable metal contaminants.

11. Multi-component adsorption • Structure or geometry of the adsorbent • Polarizability; Electronic Charge • Ionic radius The relative ionic radius might affect how well the metal ions would be sorbed onto the geometrical shape of the adsorbent micro-porous structure. This would be important when considering the effect of competition forces on adsorption.

12. Multi-component systems • Concentrations and ratios reflective of initial Bombardier filter cake

13. Results - effect of pH Effect of pH on removal of chromium at a fixed initial concentration of 180 mg/L for chromium and 20 mg/L for both aluminium and copper. (50 ml of solution contacted with 50mg of Activated Carbon (FAG400) in a shaker for seven days at 20C).

14. Results – single component Cr • Maximum capacity ≈ 100mg Cr /g GAC • Successfully modelled using Freundlich Isotherm

15. Results – binary system (Cr, Al) • Maximum capacity ≈ 80mg Cr /g GAC • Maximum capacity ≈ 40mg Al /g GAC • Al generally non highly competitive for Cr active sites

16. Results – binary system (Cr, Cu) • Maximum capacity ≈ 80mg Cr /g GAC • Maximum capacity ≈ 70mg Cu /g GAC • Cu generally non highly competitive for Cr active sites

17. Results – binary system (Al, Cu) • Maximum capacity ≈ 140mg Al /g GAC • Maximum capacity ≈ 120mg Cu /g GAC

18. Results – ternary system (Cr, Al, Cu) • Maximum capacity ≈ 80mg Cr /g GAC • Maximum capacity: Al ≈ 35mg//g; Cu ≈ 10 mg/g • Cr competitive for Al and Cu active sites

19. Ideal Adsorbed Solution (IAS) Model IAS theory assumes that the adsorption of solute species occurs simultaneously at constant spreading pressure, , and constant temperature. Single solute concentrations, X0i, are defined at the same spreading pressure as that of the mixture, i.e. 01 = 02 = mixture (1) This can then be incorporated into the Freundlich Equation to predict multi-component adsorption: (2)

20. Conclusions • Successful dissolution of Bombardier filter cake • Optimised acid dissolution 580 mg/L (< 60 seconds) • Electro-deposition  problematic • Metallic impurities (Al, Cu, Se, etc) • Low concentration (17% Cr w/w in cake) • Adsorption of Cr onto GAC • Adsorption can be optimised in low pH systems • Multi-component adsorption • Freundlich and IAS multi-component modelling

21. Future Work and Innovations • Further development of IAS model • Multi-component kinetic adsorption systems • Effect of: pH; particle size; concentration etc • Modelling of kinetic data • Reaction kinetic; diffusion models • Selective desorption of chromium • Under alkali conditions • Concentrated, single component Cr solution • Electro-deposition  problematic???

22. Recovery of metals from waste sludge/filter cakeProject QUB18/08/11 Charlie Campalani