改性硅酸钙(CSH)对重金属废水中Ni2+的吸附特性研究

以硅灰石和氧化钙为原料制备改性硅酸钙(CSH),为了探讨改性硅酸钙对Ni~(2+)的吸附特性和机理,考察了初始p H值、吸附剂投加量、初始Ni~(2+)质量浓度和硅酸钙使用次数等因素对模拟废水中Ni~(2+)去除率的影响。结果表明,p H值在3.0~6.0、吸附剂投加量为1g/L、含Ni~(2+)废水质量浓度小于200 mg/L、硅酸钙前两次使用时,CSH对Ni~(2+)均有较高的去除效果。采用Langmuir等温吸附模型拟合CSH对Ni~(2+)的吸附,得到CSH对Ni~(2+)的最大吸附量为417 mg/g。结合吸附前后的扫描电镜-能谱(SEM-EDS)和X射线衍射(XRD)图谱分析,推测出CSH的主要结构为Ca Si2O5,CSH对Ni~(2+)的吸附主要发生在CSH表面并且是通过离子交换作用进行的。通过对CSH吸附去除Ni~(2+)过程中溶液离子浓度变化的研究推断出97%的Ni~(2+)通过离子交换作用被去除,剩余的Ni~(2+)通过表面络合作用去除。

On the adsorptive behaviors of calcium silicate hydrate (CSH) to Ni2 +

The given paper is aimed at introducing a sort of novel absorptive calcium silicate hydrate(CSH) prepared from the wollastonite and calcium oxide to remove Ni2 + from the sewage with heavy metal contaminants.For the said purpose,we have first of all conducted an experiment and investigation of the effects of the original pH value,the dosage of the adsorbent,the original Ni2+ concentration and the number of times of CSH on the nickel removal,in hoping to identify and determine the optimal conditions for the Ni2+ removal.At the same time,we have also adopted the adsorption model of Langmuir so as to find the maximal CSH adsorption capacities for Ni2 + and characterize the mechanism of the adsorption process via the SEM-EDS,XRD spectrum and the changing rate of the ion concentration in the adsorptive process.The results of the aforementioned experiments have enabled us to find that the pH value is the main influential factor on the nickel adsorption.For example,the removal efficiency of CSH can all be made higher when the pH value can be made stay within a range between 3.0-6.0.In addition,the removal rate of Ni2 + can be made to reach 99％ on the condition when the adopted CSH dosage is 1 g/L and the Ni2+ concentration is lower than 200 mg/L,if the CSH is adopted for the first twice.It is also necessary to notice that,when the adsorption capacities of CSH to Ni2 + reached its utmost limit of 417 mg/g,it would be possible to use Langmuir isotherm adsorption model with its related coefficient being 0.999 3.On the other hand,based on the characterization of SEM-EDS and XRD spectrum,it can be found that the adsorption reaction that took place in the surface since the morphological status-in-situ of the CSH might have changed a great deal through the adsorption of Ni2 +.Besides,the original CSH powder might also get loosened in the process in which it turned into green and generate a lot of spherical granules on the CSH surface.Furthermore,it is also of great significance that the adsorption mechanism should be regarded as a kind of ion exchange process while the Ca peak is attenuated but the Ni peak is rising via the EDS in comparison with the original CSH.As is indicated in the XRD spectrum,the main structure of CSH may change from CaSi2O5 to NiCaSi2O6 on the surface through the ion exchange.Thus,it can be assumed that 97％ of Ni2+ has been adsorbed by the ion exchange with the rest being absorbed through the surface complexation on the basis of the variation of the ion concentrations in the adsorption process.Besides,the pH value turns to increase during the adsorption process from 6.0 to 8.6 due to the silicate hydrolysis.