Research On Adsorbability Of Waste Tea For Heavy Metals And Toxicity Assessment For Heavy Metals

In recent years, amount of heavy metal wastewater which didn't reach the discharging standard has been discharged with the rapid development of industry and caused serious heavy metal pollution. So, controlling heavy metal contamination and toxicity assessment of heavy metals have been a top priority in the environmental management.The paper which took waste Puer tea as a new type of adsorption material and Cr⁶⁺, Cu²⁺, Zn²⁺, Pb²⁺ as research subject researched the adsorbability of waste Puer tea. Through static adsorption experiment, following several aspects have been studied, including affecting factors, adsorption isotherms, adsorption kinetics and surface characteristics. Futhermore, competive adsorption among Cr⁶⁺, Cu²⁺, Zn²⁺, Pb²⁺ on the surface of waste Puer tea has been investigated. At last, the paper took Daphnia magna as experimental organism and acute toxicity of Cr⁶⁺, Cu²⁺, Zn²⁺, Pb²⁺ on Daphnia magna has been observed for toxicity assessment.Results showed that pH was the most important factor on heavy metal adsorption and the optimum pH for Cr⁶⁺ and Cu²⁺, Zn²⁺, Pb²⁺ were 2.0 and 5.0⁶.0, respectively. The adsorption rate was so fast that the adsorption amount could be up to 80%⁹0% of the equilibrium adsorption capacity in 5¹0min. The adsorption of Cr⁶⁺ onto waste tea is endothermal reaction, but the adsorption of Cu²⁺, Zn²⁺, Pb²⁺ onto waste tea was exothermic reaction. Isotherm experiments revealed that the adsorption of Cr⁶⁺, Cu²⁺, and Zn²⁺ was fitted very well to the Langmuir isotherm model. But for Pb²⁺, the adsorption data better followed the Freundlich isotherm model. Based on the coef?cient of determination R2, the adsorption kinetics of Cr⁶⁺, Cu²⁺, Zn²⁺, Pb²⁺ better followed Richie's pseudo-second order rate equation. Through the determination of Zeta-potential of waste tea, the pHZPC of waste tea was 3.8±0.1. The FTIR spectra of waste tea indicated the existence of carboxyl and amino groups etc on the surface of waste tea, which was the reason of good adsorption capability for heavy metals. The surface structure of waste tea was investigated by means of SEM, showing that well-developed pore structure existed on the surface of waste tea. Densely packed matters could be found on the surface of waste tea through SEM when Cr⁶⁺ and Pb²⁺ adsorbed, but only granular materials could be discovered when Cu²⁺ and Zn²⁺ adsorbed. The results demonstrated high adsorption capacity for Cr⁶⁺ and Pb²⁺ and low adsorption capacity for Cu²⁺ and Zn²⁺. Through the competitive adsorption experiment on the surface of waste tea, obvious Pb²⁺-Cu²⁺ antagonism, Pb²⁺-Zn²⁺ antagonism and Cu²⁺-Zn²⁺ antagonism could be observed in the competition system.The adsorption order was Pb²⁺>Cu²⁺>Zn²⁺, which was fitted to the order arranged according to electronegativity.The acute toxicity test of Cr⁶⁺, Cu²⁺, Zn²⁺, Pb²⁺ on Daphnia magna suggested that the acute toxicity order was Cu²⁺>Cr⁶⁺>Pb²⁺>Zn²⁺. Cu²⁺ was a kind of extremely toxic substance and Cr⁶⁺ belonged to highly toxic substance. The toxicity grade of Pb²⁺ and Zn²⁺ belonged to medium toxicity. The research also showed that the safe concentration of Cr⁶⁺, Cu²⁺, Zn²⁺, Pb²⁺ were 0.041 mg/L, 0.0033 mg/L, 0.66 mg/L, 0.21 mg/L, respectively.Based on above research, we can see that the waste tea adsorption technique can remove heavy metal ions in industry wastewater effectively. The new adsorption technology will show a broad application prospect in the emergency treatment of little-scale heavy metal wastewater.