Adsorbing Colloidal Flotation Removing Metals Ions in a Modified Jet Cell

Minerals Engineering 24 (2011) 1010–1015

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Minerals Engineering

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Adsorbing colloidal ﬂotation removing metals ions in a modiﬁed jet cell ⇑ ⇑ M. Santander a, , L. Valderrama a, M. Guevara a, J. Rubio b, a Departamento de Metalurgia, CRIDESAT, Universidad de Atacama (UDA), Av. Copayapu 485 Copiapó-Atacama, Chile b Laboratório de Tecnologia Mineral e Ambiental, Departamento de Engenharia de Minas, PPG3M, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, Prédio 75, Porto Alegre, RS 91501-970, Brazil article info abstract

Article history: The removal of Cu2+,Zn2+ and Ni2+ ions from synthetic wastewater with a modified Jameson cell (MJC) Received 14 January 2011 was studied using adsorption colloidal flotation (ACF). A colloidal dispersion of Fe (OH)3 (formed Accepted 29 April 2011 in situ from FeCl3) at pH 11 was used as an adsorbent colloid to ensure full adsorption and precipitation. The precipitates were flocculated with polyacrylamide and hydrophobised with sodium oleate and pine oil as a frother during the flotation stage. In the modified jet cell, the downcomer was sealed at the bot- Keywords: tom with a diffuser, and the re-flotation of detached flocs and the probability of bubbles/particles capture Jet flotation was enhanced, which improved the recovery rate. As a result, the modified Jameson cell was more effi- Colloid adsorbent cient (higher loaded carrier recoveries) than the conventional jet cell (CJC) in removing heavy metals ions. Ions removal The physico-chemical characteristics, cell design and operating parameters were studied, and the removal efficiency was evaluated by monitoring the final concentration of ions in the treated effluent. The results indicated that the removal efficiencies of the MJC were approximately 95% and 98% for dilute (Cu2+,Zn2+ and Ni2+ concentration of 2 mg/L) and concentrated wastewater (25 mg/L of each ion), respectively. The optimal parameters included a Fe+3/ion ratio of 0.5 and a minimum air flow-rate/feed flow- rate ratio of 0.18. The results are discussed in terms of the physical and physico-chemical parameters, and the findings suggested that the proposed flotation technique has great potential for the treatment of wastewater. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction tion and sludge filtration. Other methods that can be used to treat effluents containing anions and dissolved heavy metals are micro/ The extraction, purification and processing of ores involves the nano/ultrafiltration, reverse osmosis, ion exchange, flotation and use of large amounts of water, which generates contaminated biosorption (absorption and/or adsorption). Some of these pro- effluents. The pollutants associated with these effluents can in- cesses have high operating costs, whereas others are inefficient clude colloidal and suspended solids, residual chemical reagents, (Silveira et al., 2009). heavy metal ions, toxic anions, oils used in machines and lubrica- Among novel toxic waste removal techniques, methods based tion (emulsified or non-emulsified) organic waste (frothers, collec- on flotation and the immobilisation of pollutants as precipitates tors and surfactants), flocculants, flotation modifiers, organic or adsorbates have potential in wastewater treatment. Some alter- solvents, and others. (Rubio, 1998; Rubio et al., 2002; Carissimi native methods for heavy metal ion removal are precipitate flota- et al., 2007; Rodrigues and Rubio, 2007). tion, adsorbing colloid flotation (ACF) and adsorbing particle When liquid wastes are generated in abandoned mining sites, flotation (APF). tailing deposits and tailing dams, the solution may be acidic (pH ACF involves the removal of metal ions by adsorption onto a is less than 7) and contain significant amounts of dissolved metals precipitate (coagula), which acts as an adsorbing carrier. The such as nickel, copper, zinc, lead, mercury, manganese and sul- loaded carrier is then floated by adding a flocculant and/or a suit- phate, among other ions (Silveira et al., 2009). able collector surfactant. Carriers that have been employed in ACF The conventional method for the removal of ions (mainly heavy include ferric or aluminium hydroxides and sodium oleate or lauryl metals) is precipitation-settling, followed by thickening, deposi- sulphate (Rubio, 1998; Alexandrova and Grigorov 1996; Stalidis et al., 1989; McIntyre et al., 1982; Carissimi et al., 2007; Rodrigues and Rubio, 2007). Several examples of studies on ACF are summa- ⇑ Corresponding authors. Tel.: +56 52 206637; fax: +56 52 206621 (M. Santan- rised in Table 1. der), tel.: +55 51 33089479; fax: +55 51 33089477 (J. Rubio). Dissolved air flotation (DAF) devices are widely used for solid/li- E-mail addresses: [email protected] (M. Santander), [email protected] (J. Rubio). quid separation. However, when large volumes of effluent must be URLs: http://www.uda.cl (M. Santander), http://www.ufrgs.br/ltm (J. Rubio). treated, this equipment presents several limitations due to its low

Table 1 ration (30–40% weight basis), DAF processes can be used to sepa- APF Process – examples of reported studies. rate solids that are present in relatively low concentrations (1– Adsorbing-carrier colloids Contaminants Author(s) 3% weight basis) (Rubio et al., 2002). DAF microbubbles are used to catch only small, light solids, such as metal-ion hydroxide flocs Fe(OH)3 Cu Choi et al. (2000) Polyaluminum chloride (PAC) Zn, Pb, Cu, Ni Huang et al. and bacteria, which have a specific weight that is similar to that of (2000) water. Namely, bubbles generated in ore flotation machines (600– FeCl3Á6H2O Zn, Cu, Cd, Pb Sabti et al. (2002) 2500 lm diameters) are not applicable for separating the afore- Fe(OH)3 or Al(OH)3 Zn, Cd Jurkiewicz (2005) +6 mentioned materials (Solari and Gochin, 1992; Rubio, 2003; Rubio Fe(OH)3 Cr ,Cu Matis et al. (2005) et al., 2002). Fe(OH)3 Cu, Cd, Pb, Ni Capponi et al. (2006) Nowadays, non-conventional flotation technologies such as Polyaluminum chloride silicate (PAX- Cu Ghazy et al. Jameson cells, columns and centrifuge cells that are used for the XL60 S) (2006) concentration of minerals are potential alternatives for the re- ZnHCF 137Cs Shakir et al. (2007) moval of ion-loaded precipitates (Clayton et al., 1991; Santander and Rubio, 1998; Santander et al., 1999). However, the mechanical strength of adsorbing colloids is too low to withstand turbulent throughput (approximately 7 m3/m2/h). In DAF, particles, oils and hydrodynamic conditions. Thus, a flocculant must be added to in- precipitate-loaded adsorbents are removed by flotation via fine crease the mechanical strength and resistance of the colloids to bubbles or microbubbles. shear stress (Pavez et al., 2000; Rubio et al., 2002). Flotation devices (and their applications) differ based on the Jameson cells have shown great potential, in mineral processing volume of air introduced during the process and the concentration solid/liquid separation and liquid/liquid separation (Jameson and of solids to be separated. For instance, compared to mineral sepa- Manlapig, 1991; Cowburn et al., 2005). The main advantage of

Fig. 1. Schematic diagram of Jet (Jameson) ﬂotation cells (a) CJC-Conventional and (b), (c) MJC- Modiﬁed Jameson cell. 1012 M. Santander et al. / Minerals Engineering 24 (2011) 1010–1015

Jameson cells is their high efficiency and moderate equipment and frother, respectively. The pH of the medium was modified with costs (Clayton et al., 1991; Harbort et al. 1994). Nevertheless, in sodium hydroxide (NaOH), and de-mineralised water was used to some cases, the rupture of fragile coagula or flocs has been ob- prepare the reagents. served in the downcomer. However, these problems have been re- cently overcome by applying low-shear mixing heads, recycling of 2.2. Flotation cells treated water and adding polymeric flocculants to the downcomer. As a result, Jameson cells can be used in wastewater treatment and The removal of loaded colloid was achieved using a conven- the recovery of solvent extraction liquors (Readett and Clayton, tional jet cell and a modified jet cell. Both lab flotation cells pos- 1993), municipal waters (Yan and Jameson, 2004) and the treat- sessed a capacity of 0.42 m3/h and consisted of a downcomer, a ment of wastes from a variety of industries, such as dairy factories, flotation tank and a level control system. The cell tank (acrylic) abattoirs, metal finishing, rolling mills and coke ovens. possessed a diameter and height of 0.145 m and 0.55 m (9 L capac- The Jameson cell provides many advantages such as a compact ity), respectively, and the froth launder was 0.3 m in diameter and design, low capital cost, no moving parts, low power consumption, 0.2 m in height. Synthetic wastewater was pumped at a flow rate of low maintenance costs, low residence times (<3 min), high 0.13 m3/h and was fed to the cells using a helical pump with a throughput and high efficiency. capacity of 0.5 m3/h. The objective of the present work was to modify the design of a jet flotation cell and study the removal efficiency of heavy metals (Cu, Ni and Zn) using ferric hydroxide as a model colloid of a carrier 2.3. Conventional Jameson cell adsorbent. The work is a continuation of a series on applications of a rapid flotation to remove pollutants (Santander et al., 2011). Fig. 1a shows a schematic diagram of the conventional Jameson cell system. The cell consisted of a downcomer (contact tube), a 50- L PVC flotation tank (phase separation) and a level control system. 2. Experimental The downcomer possessed a height and diameter of 1.8 m and 25 mm, and was equipped with an air injector (a nozzle constrictor 2.1. Materials 3 mm). The level control system was made of PVC and was used to adjust the height of the liquid in the flotation tank (height of the Synthetic effluents containing copper, nickel and zinc ions were froth layer). obtained by dissolving analytical grade CuSO4Á5H2O; NiSO4Á7H2O 3+ and ZnSO4Á6H2O in water at pH 2. Fe , which was obtained by dis- 2.4. Modified Jameson cell solving FeCl3Á6H2O in water, was used as a co-precipitant, and its hydrolysis product (Fe (OH)3) was used as an adsorbing colloidal Fig. 1b shows a schematic representation of the modified cell. precipitate. As shown in the figure, a bottom blind diffuser was placed at the Sodium polyacrylate (molecular weight = 1000,000) was use- end of the downcomer, which allowed air bubbles/flocs to move d as a flocculant (Alcotac FE4 from Ciba Specialty Chemicals), and in an upward direction towards the frothy phase. If flocs break, sodium lauryl sulphate and pine oil were used as a flocs collector the detached units can be recaptured by the rising bubbles

Fig. 2. Details of the modiﬁcation (diffuser) at the downcomer bottom of a Jameson cell. M. Santander et al. / Minerals Engineering 24 (2011) 1010–1015 1013

(Fig. 2). The other design parameters of the modiﬁed unit were 100 similar to those of the conventional Jameson cell. Modified jet cell 95 2.5. Methods 90 The model efﬂuent was prepared by dissolving different metal salts and varying the concentration of Cu2+,Zn2+ and Ni2+ in a 50-L tank of tap water (acidic medium,

(Fe(OH)3), which adsorb heavy metal ions. The performance of (%) efficiency Removal the flotation cells in the removal of copper ions were compared, and the MJC was used to separate loaded carriers from dilute 75 (2 mg/L Cu, Zn and Ni ions) and concentrated synthetic effluent 0 5 10 15 20 25 (about 24 mg/L Cu, Zn and Ni ions). Finally, the effects of the Fe/ Initial concentration Cu2+(mg/L) metal ion concentration and the air flow-rate/feed flow-rate ratio were studied. The results were expressed as the mean, which Fig. 3. Adsorbing colloidal flotation of copper ions in Jameson cells (MJC and CJC). +3 was obtained by conducting 20-min tests in triplicate. The stan- Conditions: pH 11; (Fe ) = 20 mg/L, 10 mg/L, sodium polyacrylate (flocculant), 50 mg/L sodium oleate (collector) and 10 mg/L pine oil (frother). dard error of the mean was ±5%, and the confidence interval was 95%. The pH of the solution was not increased in the absence of Fe circuit). The detached flocs cannot be re-collected and are trapped salts; otherwise, metal ions would precipitate (especially in con- by the turbulent flow-rate of the treated water. centrated solutions). In fact, whether or not precipitation would Alternatively, floc breakage appears to be diminished in the occur was difficult to ascertain due to kinetic reasons. A pH of 11 MJC. Herein, the jet is diverted in an upward direction, dispersing was selected because the colloids were larger and more consistent air bubbles/flocs throughout the separation tank, decreasing the under these conditions; however, the colloids could not withstand probability of bubble/floc detachment and allowing re-flotation. shearing. Thus, 10 mg/L of flocculant was added to prevent precip- The results shown in Fig. 3 suggested that concentration effects itate shearing and breakage problems in the injector. were not as pronounced in the MJC, and the removal rates fluctu- Thereafter, a collector and a frother were added at a concentra- ated between 95% and 99%. At an initial copper dosage of 25 mg/L, tion of 50 and 10 mg/L, respectively. The collector was required be- the final concentration of the effluent was 0.15 mg/L, which is cause the loaded colloids, now in the form of flocs, were fairly within the analytical error of the atomic absorption spectrometer. hydrophilic, and the frother was used to prevent the formation of The same effect was observed when the copper concentration was large bubbles, which create turbulence in the downcomer and equal to 2 mg/L; however, the concentration of copper in the trea- phase separation tank. The time required to achieve colloid forma- ted effluent was only 0.10 mg/L. Thus, compared to that of the CJC, tion and floc adsorption was established in preliminary studies and a 19% higher removal efficiency was attained with the MJC. was equal to 5 and 10 min, respectively. Table 3 shows the adsorbing colloidal flotation results for the In both cells, the collection (collision–adhesion) of aggregates/ removal of ions in dilute and concentrated solutions (Cu, Ni and flocs via air bubbles occurs in the downcomer, and separation oc- Zn) with the MJC, and Fig. 4 provides a detailed depiction of the curs in the flotation tank. The mixture falls, and light aerated flocs loaded froth. rise to the froth layer. Alternatively, treated water is discharged at The removal efficiencies were slightly higher for the dilute solu- the bottom of the tank. Table 2 summarises the operating param- tion than the concentrated effluent because the (Fe+3)/(Cu+2,Zn+2, eters of both cells. Ni+2) ratio was fairly low (approximately 0.26 for the loaded sam- ples). Nevertheless, as shown in Table 4, at higher (Fe+3)/(Cu+2, +2 +2 3. Results and discussion Zn ,Ni ) ratios, superior performance was observed. Thus, a minimum ratio of 0.5 was required to attain removal rates >98%. Under Fig. 3 shows the removal efficiency of copper ions in the CJC and the optimal conditions, the residual content of the ions in the trea- MJC. As shown in the figure, the removal rates of the MJC were ted effluent was always lower than those permitted by the emis- higher for the entire concentration range of Cu+2 ions. With the sion standards of Brazil for the discharge of wastewater into CJC, the removal rates were always <90%. In contrast, with the reservoirs. MJC, nearly complete removal was achieved. The results indicated that both flocculant and collector were The inferior performance of the CJC was due to the fact that necessary to achieve good separation. In the absence of these re- some air bubbles/flocs units are discharged in the jet and break agents, incomplete separation was observed due to the destruction apart in the separation tank. As a result, flocs are carried by of colloids under shearing (results not shown). entrainment towards the discharge of the clarified effluent (short The effect of the air flow-rate/feed flow-rate ratio on the metal (Cu, Zn and Ni) ion removal rate (25 mg/L of each metal ion) in the MJC was studied under constant operating conditions. The feed Table 2 flow-rate was maintained at 2140 mL/min, and the air flow rate Flotation in the jet cells. Main parameters. was varied between 133 and 862 mL/min. Parameter Values As shown in Table 5, a minimum ratio of 0.18 was required to

3 attain optimal performance (>97% metal ion removal). Namely, Flow rate (feed) 0.42 m /h Retention time in the downcomer 8 s (approximated) when the ratio was less than 0.18, the removal efficiencies de- Retention time in the flotation cell system 77 s (approximated) creased to 67%. Moreover, when the air flow-rate/feed flow-rate ra- Flotation cell volume 0.009 m3 tio was >0.35, a slight decrease in the performance was observed. 3 2 Loading capacity 24 m /m h (average) At low air flow-rates, the Sb value, or the superficial bubble sur- Air flow-rate/feed flow-rate ratio Minimum 0.18 face area flux and carrying capacity of the device were fairly low, 1014 M. Santander et al. / Minerals Engineering 24 (2011) 1010–1015

Table 3 Adsorbing colloidal ﬂotation in the MJC: Removal of ions in dilute and concentrated solutions (Cu, Ni and Zn). Conditions: pH = 11, 20 mg/L Fe+3, 10 mg/L, sodium polyacrylate (ﬂocculant), 50 mg/L sodium oleate (collector) and 10 mg/L pine oil (frother).

Initial concentration (mg/L) Final concentration (mg/L) Removal (%) Cu+2 Zn+2 Ni+2 Cu+2 Zn+2 Ni+2 Cu+2 Zn+2 Ni+2 2 2 2 0.1 0.07 0.05 95.4 96.0 98.0 24 25 24 1.2 1.31 1.10 95,0 95.0 95.4

Table 5 Adsorbing colloidal flotation in the MJC: Effect of the air flow-rate/feed flow-rate ratio on metals (Cu, Zn and Ni) ions removal (25 mg/L each metal ion). Conditions: pH 11, (Fe+3)/(ion) ratio = 0.52, 10 mg/L sodium polyacrylate (flocculant), 50 mg/L sodium oleate (collector) and 10 mg/L pine oil (frother).

Air ﬂow-rate/feed ﬂow-rate ratio Removal (%) Cu+2 Zn+2 Ni+2 0.06 63 62 62 0.18 97 96 95 0.28 98 98 97 0.35 96 96 95 0.43 95 94 93

tions of heavy metal ions (25 mg/L of Cu2+,Zn2+ and Ni2+). The residual concentration of metal ions in the treated water was lower Fig. 4. Adsorbing colloidal flotation of metal ions (Cu, Zn, Ni) in the MJC: than those permitted by Brazilian legislation. To achieve the de- Appearance of the loaded metal ions flocs carrier bearing froth layer. Conditions: sired removal efficiencies, a minimum (Fe+3)/(ion) ratio of 0.5 +3 pH 11, (Fe ) = 20 mg/L, 24 mg/L each metal ion, 10 mg/L, sodium polyacrylate and a minimum air flow-rate/feed flow-rate ratio of 0.18 are re- (flocculant), 50 mg/L sodium oleate (collector) and 10 mg/L pine oil (frother). quired. Thus, the proposed technique can be used to rapidly remove heavy metals ions from contaminated water or wastewater. Table 4 +3 Adsorbing colloidal flotation in the MJC: Effect of the Fe concentration on removal of Acknowledgements ions (25 mg/L each metal ion). Conditions: pH 11, 10 mg/L, sodium polyacrylate (flocculant), 50 mg/L sodium oleate (collector) and 10 mg/L pine oil (frother). The authors acknowledge financial support from the University +3 +3 Fe concentration, mg/L (Fe )/(ion) ratio Removal (%) of Atacama (Dirección de Investigaciones de la Universidad de Ata- Cu+2 Zn+2 Ni+2 cama, DIUDA) and appreciate the collaboration of Mr. Bruno Zazz- 10 0.13 94.4 94.5 94.3 ali in the construction of the flotation cell. 20 0.26 94.4 96.0 94.7 40 0.52 98.0 98.4 98.1 References

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