| Layered-structure silicates are important non-metallic mineral resources due to their special structures and unique properties. With the utilization of non-metallic mineral resources in the field of functional materials, more and more attention is paid to the porous materials preparation from layered silicate minerals by using mechanical activation, thermal activation, and chemical modification, etc.In this paper, preparation methods of porous materials were studied from two typical layered silicates, kaolinite and pyrophyllite, and the adsorption characters of heavy metal ions on the porous materials was characterized further.Preparation technology of porous alumina from kaolinite is: kaolinite is roasted 1150℃for 15min firstly, and the roasted kaolinite is leached with 120g/L sodium hydroxide solution under the conditions of leaching temperature 120℃, leaching time 100min and liquid to solid (L/S) ratio of 10:1. The porous alumina prepared from kaolinite has specific surface area of 55.8m2/g and the average pore diameter is 10.43nm, the pore volume is 0.1455cc/g.Preparation technology of porous alumina from pyrophyllite is: pyrophyllite is roasted at 115℃for 15min, and the roasted pyrophyllite is leached with 120g/L sodium hydroxide solution under the conditions of leaching temperature 120℃, leaching time 100min and L/S ratio of 10:1. The porous alumina prepared from pyrophyllite has specific surface area of 42.7m2/g and the average pore size is 21.14nm, the pore volume is 0.2329cc/g.Preparation technology of porous silica from kaolinite is:kaolinite is roasted at 850℃for 15min firstly, and the roasted kaolinite is leached with 20% sulfuric acid solution under the conditions of leaching temperature 120℃, leaching time 90min and L/S ratio of 10:1. The porous silica prepared from kaolinite has large specific surface area of 280.3m2/g, pore volume of 0.1945cc/g and average pore size of 2.77nm and shaped as worm-like.These porous materials all belong to the mesoporous materials. It can be founded that kaolinite and pyrophyllite under thermal treatment produce Alv structure, which can facilitate alumina dissolution in acidic solution, and the formation of amorphous SiO2 phase at high temperature is benefit for alkali dissociation. The dissolution ratio of Al2O3 and SiO2 in activated kaolinite or pyrophyllite will lead to the change of the specific surface area of porous materials. The increase of dissolution ratio makes the specific surface area larger. But there is no relationship between the average pore diameter of various materials, B JH pore size or pore volume and the dissolution ratio, so the change of dissolution ratio will not control the pore size.Adsorption tests were carried out to reveale the adsorption characters of copper, lead, cadmium, and chromium ions on different kinds of porous materials including the raw ores, roasted ores and porous materials, it can be found that the adsorption capacity of copper, lead and cadmium ions on porous alumina materials is very large, the maxium reaches 134mg/g,450mg/g and 227mg/g respectively, while the adsorption of hexavalent chromium is as small as 0.5mg/g. The copper, cadmium and lead ion concentrations can be decreased from 50mg/L, 100mg/L,50mg/L to 0.01 mg/L, 0.01mg/L,0.02mg/L, respectively.The adsorption kinetics results of copper, lead and cadmium ions on alumina porous materials show that:the adsorption kinetics of copper are followed as the rate equation of Bangham and the Langmuir adsorption isotherm; the adsorption kinetics of lead ion are followed as the Elovich rate equation and the adsorption behavior followed the Langmuir isotherm; the adsorption rate of cadmium ion is followed as the Bangham equation.These alumina porous materials'excellent performance on the adsorption of heavy metal ions for them provides a new way in the application of polluted water. |
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