Environmental Effects of Micro- and Ultra-microchannel Structures of Natural Minerals

Abstract

Abstract The micro-channels usually refers to structural channels of minerals with aperture in the range of 0.3 nm to 2.0 nm. Such microchannels include, Mn-O octahedron channel filled by K in cryptomelane, and channel constructed by Si-O and Al-O tetragonal molecular sieve filled by Na and Ca in zeolite, and effectively have the function of molecular sieve. Here we point out that ultra-microchannels of natural minerals have apertures below 0.3 nm with the features of ionic sieves. The ultra-microchannels of mineral feldspar, accounting for half mass of the Earth's crust, have been largely ignored because the aperture is too small. In this work, we present that feldspar displays a certain degree of ion exchange and owns a feature of channel structure under both high and low temperatures. At high temperature, Na+ can enter the channels of feldspars. The content of Na2O in feldspar increases up to 15.9%. At middle temperature, Pb2+ can also enter the channels of feldspar as the result of ion exchange, leading thus to the formation of Pb-feldspar. At room temperature, about 97.94% Cd2+ can be removed and Cd-feldspar can be obtained. These phenomena indicate typical effects of ultra-microchannels of feldspar, which may be suggested as a potential for the treatment of heavy metal pollution and nuclear waste. The ultra-microchannels of natural minerals have played special role in migration and exchange of geomaterials. The molecular sieves of microchannels of a few natural minerals have the property of purifying molecular gas pollution. And the ionic sieves of ultra-microchannels of most natural minerals can purify ionic water contaminates.