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Zinc is one of the environmental pollutants which are toxic even at very low concentrations. Domestic and industrial discharges are probably the two most important sources for zinc in the water environment.
Recent trends and breakthroughs in the removal of zinc from wastewater are discussed in this section. The contents include:
- Current Wastewater Treatment Process - Zinc Removal
- New Technologies in Zinc Removal from Wastewater
- Effect of Sodium Xylenesulfonate on Zinc Removal from Wastewater
- Nickel, Copper and Zinc Removal from Waste Water by A Modified Clay Sorbent
- Regeneration And Reuse of Spent Naoh-Treated Oil Palm Frond for Copper and Zinc Removal from Wastewater
- Removal of Lead, Cadmium, Zinc, and Copper from Industrial Wastewater by Carbon Developed from Walnut, Hazelnut, Almond, Pistachio Shell, and Apricot Stone
- Removal of Zinc Ion from Water by Sorption onto Iron-Based Nanoadsorbent
- Zinc Removal from Aqueous Solution Using an Industrial By-Product Phosphogypsum
- Removal of Zinc and Nickel Ions by Complexation–Membrane Filtration Process from Industrial Wastewater
- Removal of Zinc from Wastewater Using Natural and Synthetic Adsorbents
Zinc is most often found in plating and galvanizing operations. In plating shops, the zinc is often complexed with cyanide and the cyanide must be treated to free the zinc before precipitation can occur. Traditional cyanide destruct systems use sodium hypochlorite to oxidize the cyanide. Like copper, zinc can be precipitated as the hydroxide salt. Finally, it can be removed by ion exchange in methods similar to copper.
Precipitation of the insoluble hydroxide salt is the most common form of treatment. This salt is formed by adjusting the pH of the water to about 10-10.5 to form the precipitate. If cyanide is present, it must be pre-treated before entering the Hydro-Flo Technologies treatment system. When other complexing agents are present, Hydro-Flo engineers can design a treatment system using metal trapping chemistry.
Ion exchange can be used to remove zinc from wastewater. Hydro-Flo ion exchange systems are designed to treat plating rinse water with trace amounts of metals. The water is sent through cation and anion resin beds, along with activated carbon and/or media filtration to produce deionized water that can be returned to the process. The advantage offered by Hydro-Flo ion exchange systems is that the resin is regenerated on-site, eliminating the need for bottle haul off. Since the regenerate waste will contain any copper and other metals removed during treatment, a vacuum distillation system can be used to concentrate the regenerate even further to reduce the amount of liquid waste hauled away. The purified water from the vacuum distillation system can also be returned to the process.
New Technologies in Zinc Removal from WastewaterEffect of Sodium Xylenesulfonate on Zinc Removal from Wastewater
This study was conducted to evaluate the effects of sodium xylenesulfonate (SXS), a constituent of a common aqueous cleaner, on zinc removal from industrial wastewater using hydroxide precipitation. In addition, the effects of polyaluminum chloride (PAC) dosages used in the treatment plant were also evaluated. It was found that low levels of SXS did not significantly affect zinc removal. However, higher concentrations of SXS, especially when combined with greater than optimum levels of PAC, did significantly inhibit zinc removal through hydroxide precipitation.1
Nickel, Copper and Zinc Removal from Waste Water by Modified Clay Sorbent
The use of a sorbent produced by the chemical treatment of a locally available clay for the removal of some heavy metals from waste water has been investigated. The modification of the natural clay was performed by treatment with hydrochloric acid and subsequent neutralisation of the resultant solution by sodium hydroxide. The chemical and structural characteristics of the natural and modified clays were determined. The amount of iron, aluminium and magnesium compounds increased in the modified sorbent. Acidic treatment led to the decomposition of the montmorillonite structure. Sorption studies were carried out by both batch and column methods. The uptake capacity of the modified clay for nickel, copper and zinc did significantly increase. Batch and column sorption methods enabled the removal of nickel, copper and zinc ions till the permissible sewerage discharge concentration.2
Regeneration and Reuse of Spent Naoh-Treated Oil Palm Frond for Copper and Zinc Removal from Wastewater
In this study, the use of NaOH-treated oil palm frond (OPF) sorbent for Cu and Zn removal and its subsequent regeneration process are reported. The regeneration of the spent sorbent was achieved by desorbing the metals in 0.1 M of sodium hydroxide (NaOH), ethylene diamine tetraacetic acid (EDTA), hydrochloric acid (HCl) and nitric acid (HNO3) solutions. The reusability study of the sorbent was conducted using 100 mg/l of Cu and Zn at a pH of 4.5 and 5.5, respectively for 1 h. The results were to be correlated with the mechanism of the metal uptake. Freundlich isotherm fitted the data to indicate the presence of heterogeneous metal sorption sites. Zn showed better regeneration efficiency of up to 88% and HCl was the best regeneration agent. The results confirmed that ion exchange was the main mechanism for the metal uptake. The desorption efficiency dropped by merely about 20% while the sorption capacity experienced a drastic drop after reuse for the fourth cycle. The damage occurred on the heavy metal binding sites by the strong acid was responsible for this drop.3
Removal of Lead, Cadmium, Zinc, and Copper from Industrial Wastewater by Carbon Developed from Walnut, Hazelnut, Almond, Pistachio Shell, and Apricot Stone
In this work, adsorption of copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) that exist in industrial wastewater onto the carbon produced from nutshells of walnut, hazelnut, pistachio, almond, and apricot stone has been investigated. All the agricultural shell or stone used were ground, sieved to a defined size range, and carbonized in an oven. Time and temperature of heating were optimized at 15 min and 800 °C, respectively, to reach maximum removal efficiency. Removal efficiency was optimized regarding to the initial pH, flow rate, and dose of adsorbent. The maximum removal occurred at pH 6–10, flow rate of 3 mL/min, and 0.1 g of the adsorbent. Capacity of carbon sources for removing cations will be considerably decreased in the following times of passing through them. Results showed that the cations studied significantly can be removed by the carbon sources. Efficiency of carbon to remove the cations from real wastewater produced by copper industries was also studied. Finding showed that not only these cations can be removed considerably by the carbon sources noted above, but also removing efficiency are much more in the real samples. These results were in adoption to those obtained by standard mixture synthetic wastewater.4
Removal of Zinc Ion from Water by Sorption onto Iron-Based Nanoadsorbent
Batch and column experiments were conducted to investigate zinc removal from dilute aqueous solution (i.e. effluent) by sorption onto synthetic nanocrystalline akaganéite. The effects of adsorbent amount, zinc concentration, solution pH value, ionic strength and temperature variation on the treatment process were mainly investigated during this study. Typical adsorption models were determined searching the mechanism of sorption while the bed depth-service time model was applied to column (with granular material) experiments.5
Zinc Removal from Aqueous Solution Using an Industrial By-Product Phosphogypsum
The removal of zinc(II) ions from aqueous medium by phosphogypsum was examined. The removal capacity of phosphogypsum for zinc(II) ions was studied as a function of solution pH, contact time, adsorbent dosage and adsorbate concentration. Phosphogypsum was pre-conditioned with lime milk before the adsorption studies. The maximum adsorption of the zinc(II) ions on the phosphogypsum was observed at the pH values between 9.0 and 10.0. It was observed that the adsorption equilibrium was reached in 40 min and the adsorption data fitted well to Freundlich model. The adsorption capacity of phosphogypsum for zinc(II) ions was determined to be 2.57 mg g−1. The results showed that the phoshogypsum is a suitable adsorbent for the removal of zinc(II) ions from aqueous solutions.6
Removal of Zinc and Nickel Ions by Complexation–Membrane Filtration Process from Industrial Wastewater
Many industrial wastewater streams contain toxic metal cations, for example, Ni2+, Zn2+, etc. or their oxyanions in up to few hundred mg/dm3, which must be removed before water recycling or discharging directly into surface waters. The conventional processes to treat this kind of wastewater are, e.g. chemical precipitation, ion exchange, membrane separations (such as electrodialysis, nanofiltration, reverse osmosis and ultrafiltration), adsorption or biosorption. In this work a membrane technique, ultrafiltration, completed with complexation was investigated.During the experiments, impact of conditions of membrane, pH and polymer/metal ratio have been investigated. The study series were carried out both of zinc and nickel. According to our studies, the most effective composition both tested metals is the following: PES-10 membrane, PAA complexation agent and pH>8. The volume ratio of the polymer bounding agent and metal ion because of environmental and economical aspects should be about unit.7
Removal of Zinc from Wastewater Using Natural and Synthetic Adsorbents
Several methods are utilized to remove zinc from industrial wastewater in which adsorption is the most versatile and widely used method. In the present work the ability of both natural and synthetic adsorbents were investigated to remove Zn(II) from wastewater. Neem bark, rice husk ash, clarified sludge and activated alumina were used for adsorption studies. The effect of different parameters such as contact time, solution pH, adsorbent dose and initial Zn(II) concentration were evaluated in terms of percent zinc removal. Clarified sludge, activated alumina and neem bark showed better adsorption behavior at acidic pH (5.0) whereas rice husk ash provided higher adsorption at alkaline pH(7.0-9.0) The equilibrium time was achieved after 5 h for rice husk ash and neem bark, 4 h for activated alumina and 2 h for clarified sludge. The kinetics of the Zn(II) adsorption on different adsorbents was found to follow first order rate mechanism. The highest and lowest rate constant was achieved for clarified sludge (22.85x10-2) and neem bark (0.28x10-2) respectively at 300C. Freundlich adsorption isotherm was well followed by all the adsorbents. Clarified sludge was the most effective adsorbent for Zn (II) removal. The optimum pH was 5.0 and equilibrium time was achieved after 2 h. First order rate equation and Freundlich adsorption isotherm was followed.8
1Robert B. Saari, John S. Stansbury, Frederic C. Laquer, 1998. Effect of Sodium Xylenesulfonate on Zinc Removal from Wastewater. Journal of Environmental Engineering, 124 (939-944).
2Vengris T, Binkien R and Sveikauskait A, 2001. Nickel, copper and zinc removal from waste water by a modified clay sorbent. Applied Clay Science, 18 (183- 190).
3Salamatiniaaet. B., et al., 2010. Regeneration and reuse of spent NaOH-treated oil palm frond for copper and zinc removal from wastewater. Chemical Engineering Journal, Vol 156 (1), pp 141-145
4Kazemipoura. M.,2008, Removal of lead, cadmium, zinc, and copper from industrial wastewater by carbon developed from walnut, hazelnut, almond, pistachio shell, and apricot stone. Journal of Hazardous Materials, Vol 150(2), pp322-327
5Deliyanni E.A.,Pelekaa E.N., and Matisa.K.A.,2007,Removal of zinc ion from water by sorption onto iron-based nanoadsorbent, Journal of Hazardous Materials, Vol141(1),pp 176-184
6Hasan Cesura and Nilgün Balkayab, 2007,Zinc removal from aqueous solution using an industrial by-product phosphogypsum,Chemical Engineering Journal, Vol 131(1-3), pp 203-208.
7Borbelya.G., and Nagy.E.,2009,Removal of zinc and nickel ions by complexation–membrane filtration process from industrial wastewater,Desalination, Vol 240 (1-3),pp 218-226
8Putting Theory into Practice: Transferring Creativity into Community Wisdom III (2008), http://dspace.cc.uregina.ca/dspace/handle/10294/1606