Study On The Adsorption Capability Of The Modified Kaolin To Heavy Metal Ions From Waste Water

Heavy metal is one of the key contaminates impacting on environment and human health.Thus,it has attracted the public attention,for example,China government makes the environmental policy and standards for the wastewater disposition.Nowadays,there are many methods and techniques used to remove heavy metal ions in wastewater,while adsorption is one of the useful techniques with a low cost and easy operation.As green adsorbents,natural mineral material is a potential and useful technique to remove heavy meat ions from wastewater.Hence in my thesis,firstly,original kaolin used to remove multi-metal ions was investigated and the result indicated that Pb²⁺,Cd²⁺,Ni²⁺,Cu²⁺,could be removed,while Cr（Ⅵ） almost was not.Among of them,the removal effcicy for Pb²⁺ was the best. However,the adsorption capacity was still low(2.1 mg·g^-1);Secondly,to further improve the adsorption capacity,the kaolin was baked with aluminum sulfate and also compared with natural kaolin,the adsorption capability of modified kaolin was significantly improved.The adsorption capability of Pb²⁺ was 18.5 mg·g^-1 using 0.5 g of modified kaolin when adsorption time was 1 hour,pH 4～5,sodium nitrate concentration 0.01 mol·L^-1,and initial Pb²⁺ concentration of 500 mg·L^-1.In contrast,the capability of natural kaolin was less than 4 mg·g^-1 under the same conditions.The surface area of modified kaolin increased from 3.35 m²·g^-1 to 9.53 m²·g^-1 and the cation exchange capability increased from 95 mmol·kg^-1 to 236 mmol·kg^-1,leading to the improvement of adsorption capability.Furthermore,a less than 10 mg·L^-1 Pb²⁺ in real wastewater was achieved after treated using the modified kaolin,which was agreement with the standard policy set up by the China EPA,but natural kaolin was not.The regeneration of modified kaolin was also examined;Finally,the removal of Cr（Ⅵ） was tested using modified kaolin with a organic surfactant such as HDTMA.The results show that the adsorption capability of 0.5 g kaolin modified with 2.0%HDTMA to Cr（Ⅵ） was 5.2 mg·g^-1 when the conditions were the time 1 hour,pH 3～6,sodium nitrate concentration 0.01 mol·L^-1 and initial Cr（Ⅵ） concentration of 250 mg·L^-1.It is about 8 times as that(0.66 mg·g^-1) of the natural kaolin.The results obtained from infrared spectra shows that HDTMA combined with kaolin layers effectively,which enhanced the adsorption capability of Cr（Ⅵ） by modified kaolin with HDTMA.A 20 mL containing 13 mg·L^-1 of Cr（Ⅵ） in real wastewater was treated by using 0.5 g organic kaolin and reduced to the residual concentration of 0.41 mg·L^-1,which did meet the requirement of the china EPA.It was also found that the organic kaolin could be utilized circularly and the efficiency still achieved 64.4 percent when used by the third time after being used with 0.01 mol·L^-1 HCl for desorption.