Batch zinc removal from aqueous solution using dried animal bones

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Abstract

The effectiveness of animal bones (AB) to adsorb zinc from aqueous solution was studied. Batch kinetics and isotherm studies were carried out to investigate the effect of contact time, initial concentration of the adsorbate, particle size, temperature, pH, and the addition of salt (NaCl) on this adsorption process. It was noted that an increase in the zinc concentration, temperature, and initial pH of the metal solution resulted in an increase in the metal uptake per unit weight of the sorbent. The decrease in the particle size of the sorbent resulted in an increase in the metal uptake per unit weight of the sorbent. The concentration of salt in the metal solution showed significant influence on the zinc ion sorption by the sorbent. Freundlich and Langmuir isotherm models were found to be applicable for the experimental data of Zn2+ sorption by AB. Desorption of metals from pre-loaded AB with zinc ions was carried out with different acid eluants and it was found that H2SO4 is the most effective desorbent.

Introduction

Zinc pollution is a very serious environmental problem. There are several sources of water pollution by zinc, such as petrochemicals, fertilizer, petroleum refining and steam generation power plant [1]. The harmful effects of zinc are due to the diseases resulted from it, for example an irritant to the skin causing itching and dermatitis, and it may also causes kertinization of the hands and soles of the feet [2]. Having in mind the adverse effects of zinc, and other heavy metals, environmental agencies set permissible limits for their levels in drinking water and other types of waters. For example according to World Health Organization (WHO), the permissible limit of Zn2+ is 3 ppm [3].

Considering the harmful effects of heavy metals, it is necessary to remove them from liquid wastes at least to a limit accepted by national and international regulatory agencies before their discharge to the environment. Several methods have been suggested for the removal of toxic metals from wastewater. These include precipitation, complexation, ion exchange and adsorption.

The use of adsorbents, e.g. activated carbon and ion exchange resins to remove trace metals from aqueous systems has been widely investigated [4], [5], [6]. Because of the high capital and regeneration costs of activated carbon and ion-exchange resins [7], researchers were encouraged to look for other types of adsorbents. Therefore, for the last decade, research has involved materials of biological origins and many forms of biomass have been shown to be effective for the removal of heavy metals [8], [9], [10]. The uptake of metals by these materials was attributed to their constituents of carbohydrates, proteins and lignin which contain functional groups, such as carboxyl, hydroxyl and amine groups, that are responsible for metal sorption [11]. Therefore, biosorption is a physio-chemical binding of a substance, sorbate, to a biological material. For example, Aksu and Kutsal [12] used the biomass Chlorella vulgaris for the removal of lead ions from wastewater, Baldry and Dean [13] used Escherichia coli to sorb copper ions from aqueous solutions. There are also investigators who used agricultural and animal waste materials as biological sorbents. Al-Asheh and Duvnjak [14] used Canola meal, a by-product of Canola oil production from Canola seeds, to remove various heavy metal ions from their aqueous solutions and Lee et al. [15] used Crab shell as animal sorbent for the removal of lead from aqueous solution.

In this work, a new biosorbent from animal origin, bones, will be considered for the recovery of heavy metals. The effect of different operating parameters, such as concentration of heavy metals, initial pH, temperature, particle size, addition of salt (NaCl) on the sorption of zinc will be presented. Regeneration of the sorbent will be investigated using different types of eluants.

Section snippets

Adsorbent

Animal bones (AB) were collected from butchers’ shops. The bones were cleaned from meat and fat and then washed with tap water for several times. Then, they were transferred to the oven at 80°C to dry. The dried bones were crushed and milled into different particle sizes in the range of 0.71–2.0 mm and were later used in the sorption tests. It is worth mentioning that no storage problem of the dried ground bones such as bacterial contamination was observed during the coarse of experiments which

Results and discussion

In this research, the use of AB for the uptake of zinc was examined. The preliminary results indicated that after 96 h of adsorption time, the uptake of Zn2+ by bones was 0.1764 mmol/g, when the initial concentration of metal was 0.918 mmol/l and the sorbent concentration was 4 mg/ml. This gives a removal of 77%.

The effect of the initial metal concentration on its uptake, which would give an indication of the sorption capacity of the new sorbent, was tested in Zn2+ solutions with concentrations

Conclusions

This study showed that animals’ bones could be used as a sorbent for the removal of Zn2+ ions from aqueous solutions. It was noticed that an increase in the metal concentration or an increase in the initial pH of the metal solution or an increase in the temperature of metal solution resulted in an increase of zinc sorption. It was noticed that the decrease in the particle size of the sorbent resulted in an increase of zinc sorption. Addition of salt showed inhibition effect on this sorption

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