Biosorption of cadmium and lead from aqueous solutions using Spirogyra

Biosorption of cadmium and lead from aqueous solutions using Spirogyra

Abstract
The aim of this study is use of Spirogyra algae for investigate its application to remove cadmium and lead from the aquatic environment. The impact of pH, contact time, initial concentration and adsorbent dosage on the adsorption the lead and cadmium examined and the optimal values of these parameters were determined. The results showed that 3 g/l Spirogyra algae can remove 83.5 percent cadmium within 30 minutes with initial concentration of 2 mg/l at pH =6; Also, the algae with the amount of 4 g/l to 75.84% lead removal in pH =5, with initial concentration of 2 mg/l over a period of time is 40 minutes. Check isotherm and kinetic equations showed that the adsorption of cadmium and lead by algae Spirogyra the Freundlich model with a correlation coefficient 0.9914 and 0.9816 respectively and pseudo-second-order kinetic model compliance with the values of coefficients 0.9913 and 0.9872. Results showed that algae Spirogyra can be used as an adsorbent effective and environmentally sound removal of cadmium and lead used in aquatic environments.
Key words: Spirogyra algae, cadmium, lead, aquatic environment, adsorption isotherms

1. Introduction
Heavy metals are the most important pollutants for the environment and human and are a serious threat because these elements have properties such as toxicity and carcinogenicity. Heavy metals are accounted to cause universal and serious issues that have very high toxicity for the health of human being as well as environment. Though heavy metals are classified into two groups of essential and non-essential elements, nickel, iron, copper, zinc and manganese are namely the essential elements required for growth and development of plants, but cadmium is not essential for the living beings.The aim of this study is use of Spirogyra algae for investigate its application to remove cadmium and lead from the aquatic environment.

2. Material and methods
2. 1. Preparation spirogyra algae
Biomass was collected from a subterranean Birjand city. Then washed with distilled water and remove the dirt direction of reducing the amount of water was filtered by the filter paper. Biomass for 4 days after it was exposed to sunlight and Followed by oven dried at 70°C for 24 hours. Finally biomass was sifting to particles with a size between 150 to 250 mesh.


2. 2. Cadmium and lead adsorption experiments
The stock solutions of cadmium and lead (1000 mg/L) using cadmium nitrate and lead nitrate dissolve in deionized water were prepared. Then the standard solution in order to perform experiments using dilute the stock solution was prepared. At first in order to determine the optimal pH, dissolved in 6 ml Erlenmeyer flasks 50(ml) metal cadmium initial concentration of 3 (mg/l) and 6 other Erlen containing 50 (ml) of solution with initial concentration of 3 mg of lead ions shed. And using 0/1 normal NaOH solutions of and HNO3 at pH 3, 4, 5, 6, 7 and 8 set, to each amount of adsorbent was added 3 (g/l). Solution for 30 minutes at 200 revolutions per minute on a shaker device was and after passing through Whatman filter paper has been that in the liquid fraction dissolved was separated from the solid part. Finally the concentration of pollution this solution was conducted by atomic absorption.
Order to check the call time, 3(g/l) of adsorbent was taken and 50 (ml) of 3 (mg/l) of lead and cadmium solutions under conditions of pH optimum duration of 10, 20, 30, 40, 60 and 90 minutes was mixed and the amounts of cadmium and lead ions absorbed by the absorbent during this time were measured by atomic absorption spectrometry.
To determine the optimal amount of absorbent, the values 1, 2, 3, 4, 5 and 6 (g/l) to 50 (ml) of solution of cadmium and lead were added. This step was performed at pH optimum contact time. At the end, after filtering and separating the solid phase by atomic absorption spectrometry was used to measure the absorption rate.
In order to determine the optimal concentration of cadmium and lead ions, dissolved in 50 (ml) in concentrations of 0.5, 1, 2, 3, 4 and 5 mg/l of cadmium
3. Results and Discussion
Results related to the influence solution pH on cadmium and lead ions shows the minimum efficiency of adsorption of cadmium and lead equal to 42.15 percent and 37.15 respectively that happened in pH =3.The lead and cadmium uptake pattern by increasing the pH ascending finds. Then the pH above 6 performance absorption process is reduced, so pH=6 and pH=5 for cadmium and lead were determined as an optimal pH.
Results related to the influence contact time on cadmium and lead removal efficiency shows that the highest absorption rate at the initial time has taken place this is identified the speed and high ability adsorbents in the removal of cadmium ions are and lead. According to the results maximum removal time of 30 and 40 minutes for cadmium and lead were obtained.
According to results by increasing the amount of absorbent, absorption percentage of cadmium ions lead increases. Because increased adsorbents, the number of places available absorption increases. But this process reached a certain size of absorption against certain concentrations of cadmium lead continues and after it was changed to increase the amount of absorption isn’t observed in the absorption. Lead and cadmium remove this increase due to an increase in the number of places available is absorbed. With increasing concentrations of cadmium and lead ions removal efficiency is reduced. So that the concentration of 5(mg/l) the lowest level reaches. Reason for this because of decreased absorption of active sites on the surface is absorbent. In the present study with increasing the initial concentration of this heavy metals cadmium, lead removal efficiency is reduced. In fact, the results of this research showed that lead and cadmium removal efficiency with initial concentration is inversely; The reason for this is that the absorbers have a limited number of active sites are saturated at high concentrations.
Tests results the Langmuir isotherm models, Freundlich and Temkin showed a high correlation coefficients for all studied there isotherms; But according to the data, Freundlich model for cadmium and lead has the highest correlation coefficient, that respectively the amounts of are 0.9914 and 0.9816. Thus it can be concluded that cadmium and lead uptake by the spirogyra algae Process Balance data better follow Freundlich model.
4. Conclusion
Results of this research showed that under the optimum conditions the highest removal efficiency cadmium (83.5%) at pH of 6, with initial concentration of 2 (mg/l) and 3 (g/l) the adsorbent for 30 minutes and the highest percentage of removal of lead (75.84) at pH of 5 for 40 minutes with initial concentration of 2 (mg/l) and 4 (g/l) adsorbent happened. Compare isotherm models Langmuir, Freundlich and Temkin adsorption process showed that Freundlich model better of cadmium and lead follow. Also results of kinetic studies showed that removal of cadmium and lead from pseudo-quadratic models comply. In general, the results of this study showed that the algae spirogyra efficiency and high ability in remove heavy metals cadmium and lead from has its aquatic environment.