Presentation on theme: "Biosorption of metals from gold mine wastewaters by Penicillium Simplicissimum immobilised on zeolite E.N. Bakatula, E.M. Cukrowksa, I.M. Weiersbye, C.J."— Presentation transcript:
Biosorption of metals from gold mine wastewaters by Penicillium Simplicissimum immobilised on zeolite E.N. Bakatula, E.M. Cukrowksa, I.M. Weiersbye, C.J. Straker, H. Tutu University of the Witwatersrand, Johannesburg, South Africa
More than tons of gold mined leaving behind more than 244 mine tailings dumps. More than tons of gold still remain in deep resources billion tons of mine waste ~30 million tons of sulphur (Witkowski and Weiersbye, 1998) ~ tons of low-grade uranium (Winde et al., 2004) Over 70 minerals have been identified in the primary ores: quartz, pyrite, pyrrhotite, galena, arsenopyrite, gersdofite, sphalerite, urananite…
The Weekender 2008/05/03 Rising tide of acid mine water threatens Johannesburg “The water is currently around 600 m below the city’s surface but is rising at a rate of between 0.4 and 0.9 m per day” - Telegraph, 6 Sep Telegraph, 6 Sep 2010
Acid mine drainage Acid mine drainage 2FeS 2 + 7O 2 + 2H 2 O => 2FeSO 4 + 2H 2 SO 4 4FeSO 4 + O 2 + 4H 2 O => 2Fe 2 O 3 + 4H 2 SO 4 Neutralisation CaCO 3 + H 2 SO 4 => CaSO 4 + H 2 O + CO 2 Cyanidation of gold-bearing ores (Elsner’s equation): Cyanidation of gold-bearing ores (Elsner’s equation): 4Au + 8CN - + O 2 + 2H 2 O => 4Au(CN) OH - 4Au + 8CN - + O 2 + 2H 2 O => 4Au(CN) OH - Gold extraction
Water from slimes dam collected in water retain reservoirs (Courtesy: Prof. T.S. McCarthy)
Broken down pumps result in leakage of contaminated water to natural water bodies Elevated elements include S, Mg, U, Fe, Cu, Mn, Zn, Pb, Ni, As, Cr, U (Coetzee et al., 2003; Naicker et al., 2005; Tutu et al., 2008).
To underlying aquifer Seepage and surface flow Evaporation “Reactive transport modelling” Leached solution + Solid minerals → Predicted solution + “New” contact solution “New” predicted solution
Barriers for containment of toxic elements Precipitation barrier e.g. liming to precipitate elements, pH dependent Evaporation barrier e.g. evaporation of salt-laden shallow groundwater Redox barrier e.g. precipitating elements using redox differentials Adsorption barrier e.g. can be natural or engineered e.g. reactive barriers
Biosorptive properties of fungi: Penicillium simp. Biosorption - property of biomaterials as bacteria, yeast, fungi, agriculture wastes, etc. to bind and to concentrate metals from aqueous solutions by active (metabolically) and passive modes (physico-chemical pathways) Metal sorption and accumulation depends on diverse factors, such as pH, temperature, organic matter, ionic speciation and the presence of other ions in solution which may be in competition, etc. Many potential binding sites are present in fungal cell walls, including chitin, amino, carboxyl, phosphate, sulfhydryl and other functional groups, which may act individually or synergistically to bind cations.
Zeolite structure is mainly composed of 3 components: alumino-silicate framework (with a repeating pore network), exchange cations and water within the pores. Both Si/Al ratio and the cation contents determine the properties of most zeolites. The general formula is: (M 2 +, M 2+ )O. Al 2 O 3. gSiO 2. zH 2 O They have a net negative charge due to isomorphous replacement of Si 4+ by Al 3+ and this negative charge is balanced by the extra-framework cations (Na +, K +, Ca 2+ and Mg 2+ ). M + = Na + or K + ; M 2+ = Mg 2 +, Ca 2 + or Fe 2 + Structure of zeolite Structure of zeolite
Two main mechanisms are attributed to heavy metal removal by natural zeolites: (i) ion exchange and (ii) adsorption Ion exchange properties of zeolites are due to the weakly bonded extra-framework cations which are mobile and easily exchanged with solution cations. It is a good adsorbent and ion-exchange agent which is determined by its unique structure and large specific surface area. Thus, it has found wide applications in wastewater treatment research. The zeolite was selected due to its capacity for immobilising micro-organisms and to its large surface area.
EXPERIMENTAL WORK Penicillium simpliccissimum was maintained on the following solid media: 40 g L -1 Potato Dextrose Agar (PDA) and 50 g L -1 Malt Extract Agar (MEA). For experimental purpose, cultures were grown at 25 o C in liquid medium at pH 2 to 7, comprising the following: (NH 4 ) 2 SO 4, KCl, MgSO 4.7H 2 O, EDTA-Fe, ZnSO 4.7H 2 O, MnSO 4.H 2 O, CaCl 2.2H 2 O, K 2 HPO 4, yeast, glucose in 1 L of sterilised deionised water. 1 g of zeolite was added to the medium, the mixture was inoculated after autoclaving. The immobilized biomass was separated from the broth by filtration and washed with deionised water.
Penicillium simp. strains Light Microscopy (100X) Growth of penic.simp. after 5 days Penicillium strains are halotolerants (able to grow in presence or absence of salt).
Batch and column sorption experiments were done in living as well as inactive biomass for Co, Cu, Fe, Hg, Cr, Ni, U and Zn metals (single and multi- component solutions). The concentrations of metals remaining in solution were determined using ICP-OES.
RESULTS AND DISCUSSION
Zeolite – Composition and characteristics XRF characterisation of zeolite ConstituentValue (%) Si O Al 2 O Fe 2 O FeO0.08 MnO0.01 MgO0.06 CaO0.03 Na 2 O19.92 K2OK2O0.25 TiO P2O5P2O H2OH2O6.1 Surface area: 69 m 2 /g Average pore volume : cm 3 /g Average pore diameter: 150 Å CEC: meq/100 g
Penicillium simp.Zeolite-Penicillium simp. Growth curves for Penicillium simp. The growth of fungus showed ~ 10-fold increase in biomass when immobilized on zeolite (600 mg/g at pH 4).
Elemental analysis of the biomass CECCHNS meq/100 g%% Zeolite- Fungi Natural zeolite n.d Characterization of the biomass SEM analysis revealed that the biofilm covered uniformly the zeolite surface. Infrared spectra of the biomass pointed to more compounds released after 10 days of inoculation and confirmed the presence of functional groups which include: hydroxyl, carbonyl, carboxyl, amine, imidazole, phosphate groups. The % of C was high in the biomass; these results confirm the presence of organic compounds released by the fungi as revealed by with the IR spectra.
Adsorption studies Kinetic models and sorption isotherms Mathematical models (Pseudo 1 st and 2 nd order and Intraparticle diffusion models) were employed for the prediction and comparison of the binding capacity and to design the sorption process. The ‘isotherm’, a curve describing the retention of a substance on a solid at various concentrations, is a major tool to describe and predict the mobility of this substance in the environment. Langmuir and Freundlich isotherms are the most commonly used. Models have an important role in technology transfer from a laboratory scale to industrial scale.
Effect of contact time (Zeolite-Living fungi) Kinetics Adsorption studies….. Single component syst: Ci = 100 mg/L pH 3 (2.5 g in 500 mL) Multi component syst: Ci = 100 mg/L pH 3 (2.5 g in 500 mL) Kinetics Equilibrium The biosorption was fast (10 minutes) and the kinetics includes 2 phases: (1) associated with the external cell surface and (2) intra-cellular accumulation/ reaction depending on the cellular metabolism.
Effect of contact time (Zeolite-Inactive fungi) Kinetics Multi components syst: Ci = 100 mg/L pH 3 (2.5 g in 500 mL) Single component syst: Ci = 100 mg/L pH 3 (2.5 g in 500 mL) Inactive microbial biomass frequently exhibits a higher affinity for metal ions than viable cells, probably due to the absence of competing protons produced during metabolism.
Kinetics of metal ion sorption governs the rate, which determines the residence time and it is one of the important characteristics defining the efficiency of an adsorbent. Metal ions Pseudo first-order parameters Pseudo second-order parameters Intraparticle diffusion parameters qeqe K 1 /[min -1 ]R2R2 qeqe K 2 /[g mg -1 min -1 ] R2R2 K id /[mg g min] CR2R2 Cu Co Cr Fe Hg Ni UO Zn The pseudo 2 nd order model (dqt / dt = k 2 (qe – qt) 2 fits better the biosorption kinetics. Kinetic models (Zeolite – Inactive fungi)
The film diffusion coefficient was in the range of 2.03 x and 3 x cm 2 /s for the metals studied. The pore diffusion coefficient was between 3.55 x and 0.52 x cm 2 /s. The metal diffusion through the film is the rate limiting step. According to Michelson: D f = cm 2 /s and D p = cm 2 /s. The film and pore diffusion equations (D f = 0.23 r 0 δ q e / t ½ and D p = 0.03 r 0 2 / t ½ ) were used to check whether the diffusion step controlled ion exchange or not. The film and pore diffusion equations (D f = 0.23 r 0 δ q e / t ½ and D p = 0.03 r 0 2 / t ½ ) were used to check whether the diffusion step controlled ion exchange or not. D f = the film diffusion coefficient (cm 2 /s), D p = the pore diffusion coefficient (cm 2 /s), r 0 = the radius of zeolite, δ = the film thickness (0,001 cm, assuming the geometry of the spherical particles) and t ½ is the half time for the ion- exchange process (min).
Effect of pH (Zeolite-Living fungi) Isotherms Langmuir and Freundlich isotherms were used to fit the experimental data. Single component syst: Ci = 500 mg/L Multi-component syst: Ci = 500 mg/L An increase of AC was observed for U at pH 5 which is close to its hydrolysis pH. (1 g in 100 mL)
Nickel species distribution using Medusa software
Effect of pH (Zeolite-Inactive fungi) Isotherms Single component syst: Ci = 500 mg/L (1 g in 100 mL) Multi-component syst: Ci = 500 mg/L (1 g in 100 mL) The presence of Fe 2+ and Zn 2+ was found to influence uranium uptake in the multi-component system. AC was constant ( mg/g) at the pH range for Cu 2+, Fe 2+, Hg 2+, Co 2+, Zn 2+.
Effect of pH (Natural zeolite) Natural zeolite, single component syst. Ci = 500 mg/L (1 g in 100 mL) Competition between cations and protons for binding sites means that sorption of metals like Cu, Cr, Ni, Co and Zn is often reduced at low pH values.
Effect of Temperature (Zeolite-Living fungi) Thermodynamics (E a, ΔG o and ΔH o calculated from the experimenta l data. ) Single component syst: Ci = 100 mg/L, pH = 3 Multicomponent syst: Ci = 100 mg/L, pH = 3 (0.5 g in 100 mL) Ea∆ H o ∆ G o kJ/mol 25 o C40 o C60 o C Cu Cr U Fe Ni Hg Co Zn Physisorption: 5 ≤ Ea ≤ 40 kJ mol -1 Chemisorption: 40 ≤ Ea ≤ 800 kJ mol -1. ΔG = -RTln K d K d = q e /C e
Effect of Temperature (Zeolite - Inactive fungi) Thermodynamics (E a, ΔG and ΔH calculated from the experimental data) Single component syst: Ci = 100 mg/L pH=3 (0.5 g in 100 mL) Multi-component syst: Ci = 100 mg/L pH = 3 (0.5 g in 100 mL) Ea∆ H ∆ G kJ/mol 25 o C40 o C60 o C Cu Cr U Fe Ni Hg Co Zn
Effect of initial concentration (Multi-component system) Zeolite-Inactive fungi, pH= 3 (1 g in 50 mL) Zeolite-Living fungi, pH= 3 (1 g in 50 mL) The metal uptake was constant for all the metals studied except for Ni, Hg and U. For these metals, the uptake decreases until an initial concentration of 200 mg/ L for Ni and Hg; 400 mg/ L for U, most probably because of the xenobiotic effect. The metal uptake was constant for all the metals studied except for Ni, Hg and U. For these metals, the uptake decreases until an initial concentration of 200 mg/ L for Ni and Hg; 400 mg/ L for U, most probably because of the xenobiotic effect.
Desorption studies Zeolite- Inactive fungi, Ci = 100 mg/L The metal loaded in the biomass can potentially be desorbed in order to regenerate the biosorbent and to reclaim valuable metals. This biosorbent was used 5 times without any loss of its adsorption properties. The metal loaded in the biomass can potentially be desorbed in order to regenerate the biosorbent and to reclaim valuable metals. This biosorbent was used 5 times without any loss of its adsorption properties.
Application on mine effluent Sampling site
SW1SW2SW3SW4Pit water pH SO 4 2- (mg/L) CiCf%CiCf%CiCf%CiCf%CiCf% Fe < DL 99.8 Ni Zn Cr < DL97.5 Hg0.30< DL99 U0.20< DL100 After treatment with the zeolite-fungi, the quality of the effluent complied with the discharge standards for industrial wastewater. Discharge standards for industrial wastewater (SAWQG) pH 6 – 9 Fe 0.3 mg L -1 Ni 0.05 mg L -1 Zn 5 mg L -1 Cr 0.01 mg L -1 Hg mg L -1 Ci = initial metal concentration (mg L -1 ) ; Cf = final conc. % = Removal % (1 g in 50 mL)
ConclusionsConclusions The biosorbent displayed good adsorption of toxic metals even at low pH values, making it an ideal sorbent for metals in effluents. Biosorption was described to be easy, safe, rapid, inexpensive and can be used to recover heavy metals at very low concentration. Non viable microbial biomass frequently exhibits a higher affinity for metal ions than viable cells, probably due to the absence of competing protons produced during metabolism. Accumulation of metals from solutions by fungi can be divided into three categories: (1) biosorption of metal ions on the surface of fungi. (1) biosorption of metal ions on the surface of fungi. (2) intracellular uptake of metal ions. (2) intracellular uptake of metal ions. (3) chemical transformation of metal ions by fungi (3) chemical transformation of metal ions by fungi In the environment, Penicillium simpl. can grow in the silica matrix (tailings dams) at low pH and adsorption of toxic metals occurs at that pH.
Outlook Application to the recovery of metal complexes (e.g. cyanide complexes) and metalloids (e.g. As) Exploring cheaper sources of silica e.g. fly ash, zeolites, liquid glass
Acknowledgements The Carnegie Corporation The National Research Foundation The Friedel Sellschop Foundation AngloGold Ashanti