Removal of acid yellow dye 17 from aqueous solutions using an activated bone char

Dyes are compounds used to color various substances like fabrics, paper, plastics, leather, food, hair, drugs, etc. The colored wastewaters of these industries are harmful to the aquatic life in rivers and lakes due to reduced light penetration and also the presence of extremely poisonous metal ions in the dye-polluted water (Ardila-Leal et al. 2021). The colorants can be classified into natural and synthetic dyes. The latter are easy to produce and are known for their fastness, which makes them more widely used than natural dyes (Yaseen & Scholz 2019). Dyes can also be classified as cationic (basic dyes), anionic (reactive and acidic dyes), and non-ionic (disperse dyes and vat dyes) (Benkhaya et al. 2020).

Color is the first indicator of contamination to be recognized in wastewater (Barka et al. 2009). Dye wastewater is usually characterized by several contaminants such as color, acids, bases, toxic compounds, and dissolved solids. Color is the most noticeable contaminant, even at very low concentrations, and it needs to be removed or decolorized before the wastewater can be discharged. Various methods for dye removal can be divided into three categories, including biological, physical, and chemical methods such as oxidation, electrochemical destruction, adsorption by activated carbon, ion exchange, membrane filtration, and coagulation (Rebah & Siddeeg 2017). Among these water treatment techniques, adsorption is superior to other techniques for water reuse in terms of initial cost, flexibility, and simplicity of design, ease of operation, and insensitivity to toxic pollutants. It also does not result in the formation of harmful substances (Mousa & Taha 2015). Adsorption is a natural process by which molecules of a dissolved compound collect on and adhere to the surface of an adsorbent solid. There are different adsorbents prepared from locally available materials, including agricultural waste, animal bones, rocks, etc. (Alemu et al. 2018; Arora 2019; Ambaye et al. 2021; Hamad & Idrus 2022). Activated carbons from different types of agricultural solid waste including bamboo, rice husk, rubber-wood, sawdust, oil palm shell, orange fruit peels, grass wastes, and corn cob have been successfully developed previously (De Gisi et al. 2016; Georgieva et al. 2020; Ghorbani et al. 2020; Loulidi et al. 2020). Rocks also have good adsorption potential for the removal of different contaminants in polluted water (Alemu et al. 2019; Lee et al. 2021; An et al. 2022). Moreover, the need to identify low-cost materials for color removal is important to retain dyeing in industrial applications (Al-Ghouti et al. 2003).

Bone char (BC) is made from cheap bovine bone waste products with a porous hydroxyapatite structure. It has been highly regarded as a green (nontoxic), effective (high adsorption potential), low cost, ease of preparation, and easily re-generable adsorbent to remove various organic and inorganic contaminants in water (Soliman & Moustafa 2020; Medellin-Castillo et al. 2021). Due to this fact, the use of BC gained increasing interest for the treatment of contaminants in polluted water. BC has been widely used in fluoride treatment processes (Alkurdi et al. 2019; Fung et al. 2021; Sawangjang et al. 2021), heavy metal (Medellin-Castillo et al. 2020; Olaoye et al. 2021), and various types of dye removal (Reynel-Avila et al. 2016; Moura et al. 2018; Cruz et al. 2020; Kadhom et al. 2020; Al-Gheethi et al. 2022).

AY-17 dye (Figure 1) is mostly used in the paper, food, and textile dyes industries. The use of acid dyes was prohibited, due to their carcinogenic nature. Although this dye has a risk to human and animal health, it remains in use, especially in the textile industry. It is also used for the production of personal care, laundry, and cleaning agents (Jedynak et al. 2019). Therefore, treatment of AY-17 dye in wastewater is very important to alleviate its impact on the environment using locally available materials like BC discarded as solid waste in landfill in many developing countries in the world (Figure 1).

The aim of this study is to investigate the removal efficiency of AY-17 dye onto ABC in a batch process under different operating conditions (pH, adsorbent dose, initial dye concentration, and contact time). Equilibrium isotherm and kinetic studies were also done in order to define the adsorption process.

Acid yellow dye 17 powder (dye content 60%; empirical chemical formula C₁₆H₁₀Cl₂N₄Na₂O₇S₂ and molecular weight 802.10 g/mol), H₃PO₄ (85%, Merck), HCl (37%, Sigma Aldrich), and NaOH (99%, Scientific Lab Chemicals) were used to adjust the pH of the solutions during adsorption experiments), distilled water (used for solution preparation and rinsing purposes). Animal bones (cows and oxen) collected from slaughterhouses in Bahir Dar City were used for the production of activated bone char (ABC). KBr was used for Fourier transform infrared spectrometry (FT-IR) spectra development of an adsorbent.

The bone samples collected from slaughterhouses were boiled to eliminate organic substances and collagen to avoid soot formation during the pyrolysis process. It was rinsed with distilled water, sun-dried, crushed using a jaw crusher, and pyrolyzed using a muffle furnace (Nabertherm B180, Germany) at 600 °C for 2 h to produce BC (Alkurdi et al. 2019). The BC produced was activated by using 1 M phosphoric acid (85%) for 24 h. Consequently, it was filtered off, rinsed with distilled water, and heated at 105 °C for 1 h to remove the water. The ABC was dried in an oven at 105 °C for 6 h, crushed using mortar and pestle, and sieved between 1 and 1.7 mm diameter size and prepared for the next adsorption steps.

The FT-IR is used to identify the functional groups that might be involved in the binding of dye ions on the surface of the adsorbent. The functional groups of the BC were determined using a FT-IR spectrometer (Spectrum 65 FT-IR, PerkinElmer) in the wavenumber range of 400–4,000 cm⁻¹. First, the prepared adsorbent was mixed with KBr (1 mg: 100 mg) and then finely pulverized and put into a pellet-forming dye to identify the functional groups present in the ABC before and after adsorption (Kulkarni et al. 2018). A scanning electron microscope (SEM – JEOL, JSM 6360 LV) was used to investigate the surface morphology of the ABC. A thin layer of sputter was coated on the adsorbent to prevent charging during SEM imaging.

1 g of the acid yellow 17 dye powder was dissolved in 1 L of distilled water to prepare a 1,000 mg/L stock solution. It was kept in dark-colored glass bottles for further batch adsorption experiments through serial dilution. Batch experiments were conducted in a series of 250-mL beakers containing 100-mL solution and adsorbent using a rotary incubator shaker at 200 rpm (Excella E-24 Model). The pH of the solution was measured with a pH meter (Jenway 430 Model). The required pH was adjusted with 0.1 M HCl or 0.1 M NaOH solution. To evaluate dye removal efficiency, the effects of adsorbent dose, contact time, pH, and initial concentrations of the dye were investigated by varying any one of the process parameters and keeping the other parameters constant. The various parameters investigated include pH in the range of 2–11, contact time of 10–150 min, initial dye concentration of 50–300 mg/L, and adsorbent dosages (10–60 g/L) (Deshannavara et al. 2021; Harja et al. 2022; Mekuria et al. 2022). After the reaction, the solution was filtered with Whatman filter paper (0.45 μm pore diameter) and the filtrate's absorbance was determined by using a UV–Vis spectrometer (Perkin Elmer Lambda 35) at a wavelength of 401.5 nm.

An adsorption isotherm focuses on the relationship between the amount of a substance adsorbed at the surface of an adsorbent in a solution at constant temperature. Adsorption isotherm studies helps to provide information about the adsorbent capacity to remove pollutants in a unit mass equation. There are two most commonly used isotherm equations (Langmuir and Freundlich) to analyze equilibrium data of solute between adsorbent and solute.

The linear plots of C_e/q_e versus C_e suggest the applicability of the Langmuir isotherms for the removal of AY-17 dye onto ABC. The values of q_max and K_L are obtained from the slopes and intercept of the linear plot of C_e/q_e versus C_e.

The R_L values indicate the favorability of adsorption: 0 < R_L < 1, favorable; R_L > 1, unfavorable; R_L = 1, linear; and R_L = 0, irreversible (Malik 2003).

The Freundlich model was used to evaluate the adsorption of AY-17 dye onto ABC. The linear plot of the Freundlich model log q_e versus log C_e indicated a correlation coefficient (R²) of 0.650 (Figure 8(b)). The K_F and n values are obtained are 3.309 and 9.099, respectively (Table 1). This indicated ABC produced a favorable condition for adsorption of AY-17 dye (Rita 2012).

The equilibrium isotherm studies of the adsorption of AY-17 dye on the ABC surface indicated that Langmuir isotherm with a better linear fitting (R² = 0.953) than the Freundlich isotherm (R² = 0.650). The separation factor (R_L) also indicated a value of 0.259, which is between 0 and 1. This indicates the adsorption is favorable (Malik 2003).

Kinetic models are used to study the mechanism of sorption and rate-controlling steps, which helps select optimum operating conditions for the full-scale batch process. The kinetic parameters provide important information to predict adsorption rate, design and model the adsorption processes (Santhi et al. 2010). The kinetics of AY-17 dye adsorption onto ABC was analyzed using pseudo-first-order and pseudo-second-order kinetic models.

The treatment of AY-17 dye using ABC was compared with other adsorbents reported in the literature. The adsorption capacities and their experimental settings are indicated in Table 3. The ABC indicated good treatment potential of AY-17 in aqueous solutions. The availability of animal bones in abundance and its simple preparation might be important for the treatment of AY-17 dye in polluted water.

This study was conducted to investigate the removal efficiency of the ABC for the removal of AY-17 dye from aqueous solutions. The results of the experiment showed that most of the dye adsorption was done in the first 30 min of contact time, and an equilibrium was reached within 120 min. Batch studies were conducted under different operating parameters such as pH, contact time, adsorbent dosage, and initial dye concentration. The highest removal efficiency (91.43%) of AY-17 dye onto ABC was observed at optimum conditions of pH 2, adsorbent dosage of 20 g/L, contact time of 120 min, and initial dye concentration of 50 mg/L. This result indicated that ABC has a high potential to remove acid yellow 17 dye from polluted water. Generally, it can be concluded that animal bones, which are discarded as waste in developing countries and found in abundance in different waste dumping sites, can be used as an alternative option for the removal of AY-17 dye from textile wastewater.

The authors are grateful to Bahir Dar University for the financial support of this study.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.