1、Removal of pollutants from acid mine wastewater using metallurgical by-product slags D. Fenga, J.S.J. van Deventer a, C. Aldrich b aDepartment of Chemical and Biomolecular Engineering, The University of Melbourne, Melbourne, Vic., 3010, Australia b Department of Chemical Engineering, University of S
2、tellenbosch, Private Bag X1, Matieland, 7602, Stellenbosch, South Africa Received in revised form 8 January 2004； accepted 12 January 2004 Abstract Theremoval of pollutants from acid mine drainage using metallurgicalby-product slags was studied in laboratory scale. Metallurgicalby-product furnace sl
3、ags were used as sorbents for metal ions and dispersed air column flotation was employed for the solid/liquid separationof the loaded slags. Batch sorption/pH/kinetic studies were conducted using simulated Cu and Pb bearing wastewater. The calcium glasstype of slags had high surface area and porosit
4、y. Promising result was succeeded from the combined process of slag sorption/flotation on thetreatment of an acid mine drainage from a South African gold mine. 2004 Elsevier B.V. All rights reserved. Keywords: Furnace slag； Sorption； Flotation； Wastewater treatment； Acid mine drainage 1. Introductio
5、n Various methods exist for the removal of toxic metalions from aqueous solution, viz. ion exchange, reverse osmosis,precipitation and adsorption, among others. Adsorptionis by far the most versatile and widely used process.Activated carbon has been the standard adsorbent for thereclamation of munic
6、ipal and industrial wastewaters. Owingto the high-cost of activated carbon, production of itslow-cost alternatives has been the focus of research in thisarea for years. These sorbents for the heavy metals sorptionranged from natural materials to industrial and agriculturalby-products, such as fly as
7、h, carbonaceous material, metaloxides, zeolites, moss, hydroxides, lignin, clays, biomass,peanut hulls, pyrite fines, goethite and coral sand.Furnace slags as metallurgical by-products are beingused as fillers or in the production of slag cement. It hasbeen reported that granulated furnace slag can
8、be convertedinto an effective adsorbent and used for the removal ofdyes 1,2 and metal ions 3,4. Alkaline-based slags asnon-conventional sorbents for various heavy metal ionscombine ion-exchange and sorption properties with anacid-neutralising ability. Acid mine water is an unavoidableby-product of t
9、he mining and mineral industry, especiallyas far as the oxidation of sulphide minerals is concerned.Acid mine waters typically contain high concentrations ofdissolved heavy metals and sulphate and can have a highturbidity and pH values as low as 2. These conditions mayprohibit discharge of untreated
10、 acid mine waters into publicstreams, as they have a detrimental effect on aquatic plantand fish life. Similarly, ground water pollution caused by thedrainage of acid mine water is an equally serious problem.Traditionally, acid mine water is neutralised by treatmentwith lime, resulting in concomitan
11、t precipitation of iron,aluminium and other metal hydroxides. However, since theminimum solubilities for the different metals usually foundin the polluted water occur at different pH values and the hydroxide precipitates are amphoteric in nature, maximum removal efficiency of mixed metals cannot be
12、achieved at asingle precipitation pH level. Conventional sorbents are notacceptable in such a mal-condition as acidic high-turbiditymine drainage. Slags can be used as low-cost adsorbentsand neutralising agents and viable alternatives to the combinationof much more expensive activated carbon or ione
13、xchange resins and lime.Slags exist often in a powdered form and are mainly appliedas dispersions. Downstream of the reaction tank, asuitable solid/liquid separation is generally necessary. Flota-tion offers various advantages for the scope of separation,compared with other processes such as filtrat
14、ion, sedimentationor centrifugation 5 and constitutes a known method ineffluent and water treatment 6,7. Combination of adsorptionand subsequent flotation has proven to be an effectivemethod for the removal of heavy metals from wastewaterstreams 810.The present study involves an examination of the s
15、orptioncapacities of two different slags for Cu and Pb removal fromwastewater streams. Batch sorption/pH/kinetic studies wereconducted in laboratory scale using simulated Cu and Pbbearing wastewater. Flotation of slags following ion sorptionoffers an effective way for solid/liquid separation. Alsore
16、ported is the successful use of the novel technique in thetreatment of an acid drainage from a gold mine. 2. Experimental work Two furnace slags, viz. iron making slag and steel makingslag, were obtained from Saldanha Steel South Africain the form of powder with a mean particle size of 24.5and 24.1
17、m, respectively. The size distribution was: 100%and100m； 90% and 45 m； 22% and 10 m； and 1.2%and 1m for the iron slag, compared to 100% and 100m；90% and 45m； 23% and 10m； and 1.5% and 1m forthe steel slag. The chemical composition of the slags expressedas oxides in mass percentage is shown in Table
18、1.The XRD spectra obtained by a DRON X-ray diffractometerindicated that the calcium glass was the major phase inthe two slags. The slags were washed with distilled waterto remove the adhering impurities for three times and driedat 200 C. The dried slags were stored in a desiccator for Experiments.HC
19、l and NaOH (analytical grade from Merck) were usedto adjust the solution pH. The Cu and Pb stock solutionswere prepared by dissolving their corresponding chloride ornitrate salts (CuCl2 5H2O and Pb(NO3)2, analytical gradefrom Merck) in distilled water. The ion concentrations instock solutions were a
20、bout 5000 mg/l. A cationic flocculant (polyamine type) was obtained from Monica, South Africa. Sodium dodecyl sulphate (analytical grade from Sigma) was used as a collector in flotation.Batch sorption experiments were carried out at an ambienttemperature of about 18 C on a roller (60 min1) using1 l
21、screwed cap plastic bottles. The sorption isotherm studieswere conducted by varying the initial ion concentrations.After a contact time of 24 h, the reaction mixture was filteredthrough a 0.45 m membrane filter (Millipore) and the filtratewas analysed for ion contents. The loading of the slagswas de
22、termined by the difference of the ion contents beforeand after adsorption equilibrium. All the kinetic experimentswere carried out at a constant temperature of 18 Cin a 1 l round bottomed transparent plastic reaction vesselimmersed in a water bath. The solution in the vessel wasagitated with a glass
23、 impeller at a fixed speed of 600 min1.All the experiments were duplicated with only the averagevalues being reported. The metal ion contents in solutions were determined byVarian Inductively Coupled Plasma (ICP). The solution pHvalues were detected by CRISON Micro pH 2000. Electrokineticmeasurement
24、s for the determination of point ofzero charge (PZC) were carried out on a Laser Zeta meter(Rank Brothers, Cambridge). The surface area of the samplewas measured by BET method on Micropores (ModelASAP 2010, Micromeritics Instrument Corporation, Norcross,GA). The common inorganic anions were determin
25、edby a DIONEX AI450 ion chromatograph with a conductingdetector. For turbidity (NTU units) measurements, a nephelometerfrom HF Instruments was used.The test flotation column was made of glass having adiameter and height of 35 and 300 mm, respectively. Thesparged air was distributed through a sinter glass with poresize 4 (1015m). The experiments were conducted at anambient temperature of 18 C. The froth was overflowedautomatically. A certain amount of surfactant was added tothe slag slurry and was allowed to condition for 2 min priorto flotation in a beaker
