Simultaneous adsorption of dyes and heavy metals from multicomponent solutions using fly ash

doi:10.1016/j.apsusc.2009.12.145

Applied Surface Science

Volume 256, Issue 17, 15 June 2010, Pages 5486-5491

https://doi.org/10.1016/j.apsusc.2009.12.145 Get rights and content

Abstract

In wastewaters originating from dye industry there are amounts of dyes (very common methyl orange, methylene blue—MB) and heavy metals (cadmium, copper, nickel mainly from the organo-metallic dyes). They tend to adsorb in a competitive process and modify the substrate. Advanced removal is usually proposed via adsorption and the use of modified fly ash as a substrate is sustainable solution. The main constituents of fly ash (silica, alumina, iron oxide and un-burned carbon), are the priority compounds which favour the heavy metal adsorption and are active sites in dyes’ adsorption processes. The paper studies the effect of MB adsorbed on the fly ash surface on the removal efficiency of cadmium, copper and nickel ionic species from complex, multi-cationic dye solutions. The adsorption efficiency and kinetics are evaluated from the complex, multicomponent systems and possible influences are discussed. High efficiencies are obtained at low heavy metal concentrations (as it is the real case for the dyes industry) whereas at medium values, competitive processes lower the individual efficiencies of copper, nickel or cadmium from mixtures.

Introduction

Dyes, pigments and heavy metals represent common and dangerous pollutants, originating in large quantities from dye manufacturing, textile as well as pulp and paper industries. They are emitted into wastewaters and produce difficult to treat water contamination, as the colour tends to persist even after the conventional removal processes. The conventional techniques used for dyes and heavy metal removal are expensive, have average efficiency and are running in sequential steps. For example, on the commercial scale the ion-exchangers and activated carbons are used, however, with certain disadvantages. The activated carbon is a great adsorbent for dyes but de-sorption and regeneration are difficult under common conditions and the overall process becomes expensive. Moreover, its efficiency in heavy metals removal is average. The modern approach towards dyes removal is connected with photo-catalysis, mainly using TiO₂-anatase.

Ion-exchange is an efficient method, with moderate selectivity since it can not only remove the heavy metal ions but exchange Ca²⁺, Mg²⁺ ions [1]. In addition, the ion-exchangers can load with dyes, thus modifying the surface and decreasing the process reversibility. These adsorbents are efficient but not fully sustainable solution.

Recent studies [2] have shown that various fly ashes with different un-burnt carbon contents collected from the power plants can be used for sequential adsorptions of methylene blue, crystal violet, methyl orange, basic dyes and CI Reactive Red 49 from aqueous solution, because the priority compounds in fly ash favour heavy metal adsorption and develop active sites in dyes adsorption processes.

A novel technology based on a single step process is proposed, combining adsorption and photo-degradation for the simultaneous removal of both pollutants. In our studies we use a waste—“fly ash (FA)” collected from CHP Brasov (Romania), which was modified with NaOH 2N, as previously described [3]. The fly ash modification process is easy, low cost and sustainable, using alkali solutions of average concentration. By combining FA with the photo-catalysts (TiO₂) and/or adsorbents (activated carbon) a complex system, capable of simultaneous treat of dyes and heavy metals is obtained [4]. Our research followed the steps concerning heavy metals removal from single cation (Cd²⁺, Cu²⁺, Ni²⁺) solutions [4], [5], simultaneous removal of cations from multi-cations solutions using FA and FA:TiO₂ mixtures in parallel with similar studies of dyes removal via photo-degradation and adsorption. Then the mixtures of single cation solutions with dye(s) were investigated for understanding the complex influence of the components on the substrates, and the changes in mechanisms and efficiencies; a group of studies targeted the results obtained in Cd²⁺ and Cu²⁺ removal, using fly ash (FA) with methyl orange modified surface and its mixtures with TiO₂ and proved that the best adsorption efficiency is registered using the mixture with 25% of TiO₂ [6]. Similar studies were carried out on fly ash modified with methylene blue, MB. The efficiency was very good, both for the cations and for the dye. A new idea was born for a complex adsorption process involving cadmium, copper and nickel ionic species from multi-cationic dye solutions. This paper presents the results of the studies on the effect of MB adsorbed on the fly ash surface on the removal efficiency of cadmium, copper and nickel ionic species from complex, multi-cationic and dye solutions.

Section snippets

The substrate

The major compounds, expressed as oxides are presented in Table 1 for the raw fly ash collected from the electro-filters of the CPH plant in Brasov (FA), Romania. The sum of the SiO₂, Al₂O₃ and Fe₂O₃ is above 70% [7], thus according to the ASTM standards, the FA is of type F.

The fly ash was washed in ultrapure water, by stirring, at room temperature, for 48 h, to remove the soluble compounds: K₂O, Na₂O, MgO and CaO. After stirring, the filtrate solution had constant pH (9.8) and conductivity

The substrates

The XRD spectra (Fig. 1) show that the major components of fly ash are: carbon (graphite), SiO₂ in various structures (cubic and rhombohedra) combined with Al₂O₃ as rhombo H, mullite (3Al₂O₃·2SiO₅), along with γ-Al₂O₃, hematite (Fe₂O₃) and CaO. Anatas TiO₂ was also traced along with cadmium and copper compounds. Except for the alumina derivatives, the major components characterizing the raw fly ash were not removed in the modifying process. The aluminium oxide components vary from one type of

Conclusions

1.
Simultaneous removal of the methylene blue dye and cadmium, copper and nickel is possible on fly ash modified with NaOH 2N. A contact time of 60 min is convenient for reaching the maximum efficiencies.
2.
The dye adsorbs on FA and, on this new surface copper exhibits a higher affinity for the active sites compared to cadmium and nickel. The reason may be the higher mobility and ionic degree of the copper tetra-hydrated complex, compared to the hexa-complexes of Cd and Ni, at the working pH of

Acknowledgments

This work was supported by the Romanian National Agency for Research in the FOTO-COMPLEX 71-047/2007 grant.

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Citation Excerpt :
The silica-rich compositions of easily available FA are a valuable source for porous additives that can be applied for membrane modification (Abdullayev et al., 2019). Due to its outstanding properties such as sphericity (1–100 μm as shown in Fig. 9), non-toxicity, porosity, lightweight property, and high strength, FA is regarded as a cost-effective material for many applications including the removal of dyes and heavy metals from wastewater, and adsorption of volatile organic compounds from the air (Kim et al., 2013; Sultana et al., 2012; Visa et al., 2010). If fly ash is not handled appropriately, it can pose serious health risks and harm the ecosphere (Sears and Zierold, 2017).
Despite water being critical for human survival, its uneven distribution, and exposure to countless sources of pollution make water shortages increasingly urgent. Membrane technology offers an efficient solution for alleviating the water shortage impact. The selectivity and permeability of membranes can be improved by incorporating additives of different nature and size scales. However, with the vast debate about the environmental and economic feasibility of the common nanoscale materials in water treatment applications, we can infer that there is a long way before the first industrial nanocomposite membrane is commercialized. This stumbling block has motivated the scientific community to search for alternative modification routes and/or materials with sustainable features. Herein, we present a pragmatic review merging the concept of sustainability, nanotechnology, and membrane technology through the application of natural additives (e.g., Clays, Arabic Gum, zeolite, lignin, Aquaporin), recycled additives (e.g., Biochar, fly ash), and recycled waste (e.g., Polyethylene Terephthalate, recycled polystyrene) for polymeric membrane synthesis and modification. Imparted features on polymeric membranes, induced by the presence of sustainable natural and waste-based materials, are scrutinized. In addition, the strategies harnessed to eliminate the hurdles associated with the application of these nano and micro size additives for composite membranes modification are elaborated. The expanding research efforts devoted recently to membrane sustainability and the prospects for these materials are discussed. The findings of the investigations reported in this work indicate that the application of natural and waste-based additives for composite membrane fabrication/modification is a nascent research area that deserves the attention of both research and industry.

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Simultaneous adsorption of dyes and heavy metals from multicomponent solutions using fly ash

Abstract

Introduction

Section snippets

The substrate

The substrates

Conclusions

Acknowledgments

Process Biochem.

Colloids Surf. A

Water Res.

Role of unburnt carbon in adsorption of dyes on fly ash

J. Chem. Technol. Biotechnol.

Adsorption mechanisms of heavy metals on fly ash with modified surface charge

Fly ash-activated carbon powder composites for dyes and heavy metals removal

Adv. Mater. Res.

Advanced wastewater treatment for heavy metals immobilisation using modified fly ash

Advanced treatment of waste water with methyl orange and heavy metals on TiO2, fly ash and their mixtures

J. Catal. Today

Advanced treatment of waste water with methyl orange and heavy metals on TiO₂, fly ash and their mixtures