Synthesis Of Merlinoite And Analcime And Its Removal Of Cd²⁺ And Pb²⁺ From Aqueous Solutions

Heavy metals such as lead and cadmium are difficult to be degraded by organisms and can do serious harm to humanbeings.Therefore,it is important to explore methods to treat heavy metals in wastewater.Zeolite,as one kind of microporous materials has good thermal stability,ion exchange capacity and adsorption capacity.Therefore,zeolite has an important application prospect in the treatment of heavy metal irons in wastewater.K-feldspar mineral is natural and cheaper raw materials with abundant reserves for synthesizing zeolite compared to silica and alumina source chemical materials.Moreover,K-feldspar is very important as potential potassium resources for preparing K-fertilizer.In this paper,the effects of adsorption time,pH value,initial concentration and temperature on the removal of Pb²⁺and Cd²⁺in aqueous solution were investigated after the successful synthesis of analcime and merlinoite using K-feldspar powders from Henan and Innermongolia separately,China.The adsorption kinetics and thermodynamic mechanism were discussed.The results will be meaningful for the treatment of Pb²⁺and Cd²⁺polluted water or agriculturial soils.It was shown that while pH=6 and T=25?,the adsorption quantity of analcime in 50mg/L Cd²⁺solution is 11.4mg/g;the adsorption quantity of analcime in 50mg/L Pb²⁺solution can reach 11.9mg/g.When pH=6 and T=25?,the adsorption quantity of merlinoite in 100mg/L Cd²⁺solution can reach 74.5mg/g;the maximum saturated adsorption quantity of119.8mg/g at 45?.Moreover,the adsorption quantity of merlinoite in 250mg/L Pb²⁺solution is up to 240mg/g,and the adsorption rate is close to 100%if pH=3 and T=25?as well.The desorption rate of saturated adsorbed merlinoite in 5%NaCl is 81%.It was founded that in the solution of Pb²⁺and Cd²⁺binary system,merlinoite tend to adsorb Pb²⁺preferentially.It was concluded that the adsorption quantity of Cd²⁺was increased with the increase of pH value,and the adsorption quantity reached the maximum when pH=6.The adsorption quantity increased rapidly with the increase of time in 10-50min,and then the adsorption amount tended to be stable,and the saturated adsorption quantity increased with the increase of temperature.The increase of initial concentration can also increase the saturated adsorption quantity of zeolite,and the initial concentration reaches a certain extent,and the saturated adsorption quantity tends to be stable.The adsorption of Pb²⁺and Cd²⁺by two kinds of zeolite conform to the pseudo-first-order kinetics,which is controlled by the diffusion and is in accordance with the Langmuir model.By calculation,it is shown that?35?S>0,?35?H>0 and?35?G<0,which proved that the adsorption was spontaneous endothermic process.Therefore,the synthesized merlinoite is more efficient and renewable Pb²⁺or Cd²⁺heavy metals adsorbent in aqueous solutions compared to the synthesized analcime.In the future,if removing Cd²⁺heavy metal from agricultural soils using the merlinoite,exchanged K⁺could be released into soils as potential nutrient elements.