The story of zeolites began in 1756 when Axel Cronstedt, a Swedish mineralogist collected a suite of well-formed crystals from a copper mine in Lapmark, Sweden. He named these minerals -ZEOLITES- which means in Greek “boiling stones” in allusion to their peculiar frothing characteristics when heated. Although nearly fifty different species of zeolites recognized over the years, only a few investigation of major geological significance were carried out.
In 1925, Weigel and Steinhof noted that once the hydration was removed, the zeolites were capable of adsorbing small size gaseous molecules and rejecting larger ones. This property was described by McBain in 1932 as “molecular sieving”.
In recent years, there are increasing amount of efforts has been directed toward the natural zeolites occurrence in sedimentary rock of volcanic origin, their valuable physical an agricultural technology. Zeolites are group of hydrated, crystalline alumino-silicates containing exchangeable cation of group IA and IIA elements such as sodium, potassium, magnesium and calcium. They can be represented by the empirical formula:
where n = cation valence, y = 2 or greater, and w = number of water molecules contained in the voids of zeolite.
Structurally, the minerals are complex inorganic polymers based on an infinitely extending framework of AlO4 and SiO4 tetrahedra linked to each other by the sharing of oxygen ions. The channels or interconnecting voids of this framework, which may amount to as much as 50 % of the zeolite by the volume, normally contain the cations and water molecules. However when a zeolite is reversibly dehydrated by heating, the cations become coordinated with the oxygen along the inner surfaces of the cavities while the crystalline structure remains intact. This leaves a porous zeolite crystal permeated with cavities interconnected by channels which have diameters ranging between 0.3 and 0.8 Å.
Zeolites are well-defined class of crystalline naturally occurring aluminosilicate minerals. They have 3 dimension structures arising from a framework of [SiO4]4- and [AlO4]5- coordination polyhedral (left) linked by all their corners. The frameworks generally are very open and containing Channels and cavities in which are located cation and water molecules (right).
Another characteristic of zeolite property arises from their molecular framework structures in that the assemblages of tetrahedral creating porous structure happens to create regular arrays of apertures. These apertures are of such a size as to be able to selectively take up some molecules into their porous structure, whilst rejecting others on the basis of their larger effective molecular dimension. This is the property of ‘molecular sieving’, largely unique to zeolites and responsible for their 1st success.
Worldwide over 1000 occurrences of zeoilites in volcanic and sedimentary rocks of volcanic origin have now been reported from more than 40 countries. Zeolite deposits have been classified into the following six types:
- Deposits which formed from volcanic material in ‘closed’ systems of ancient and present-day saline lakes;
- Deposits which formed from volcanic material in ‘open’ system of freshwater lakes or groundwater systems;
- Deposits which formed from volcanic material in near-shore or deep-sea marine environments;
- Deposits formed by low-grade burial metamorphism of volcanic and other material in thick sedimentary sequences
- Deposits formed by hydrothermal or hot springs activity;
- Deposits formed in lacustrine or marine environments without direct evidence of volcanic precursor material.
These zeolite deposits are all the result of the alteration of volcanic glass into zeolite minerals. This process occurs from the chemical reaction between saline or alkaline surface, ground or hydrothermal waters and the volcanic glass in the tuff or sediment. The most important types of deposit are the 1st two in the list above.
Bentonite Bleaching Earth
The word of Bentonite was introduced firstly on 1898 by Knight. At that time, Bentonite was used to call a mineral rock that found in Benton Shale, Wyoming, USA. O’ Driscoll (1988) informed that Bentonite is a clay which consist of some essential minerals from smectite. Most of minerals in bentonite are montmorilonite, which have general formula:
The others minerals which could be found in bentonite in small content are chrystobalite, biotite, chalcedony, calcite, analcyte, pyrite, dolomite and plagioclase. There are two kinds of bentonite, Na-Bentonite and Ca-Bentonite. The Na-Bentonite could expand its volume when mixed with water, it is used for oil and gas drilling mud. And the Ca-Bentonite is used as bleaching agent in cooking oil industries, bleaching agent in lubricant oil recycling, as catalyst, absorber, filler etc. The Ca-Bentonite in general trading is usually called as bleaching earth, fuller’s earth, bleaching clay, taylorite or soapy clay.
Coconut Shell Activated Carbon
Activated Carbon of coconut shell basis is porous solid materials which have wide surface area in the range of 700 – 1,300 m2/ gr. The material for activation process must be sellected from good coconut shell charcoal. The coconut shell has good characteristic in hardness, small & medium pore distribution, and impurities content in the intrinsic pore. In activation process need technology innovation, how to reduce the energy cost as the biggest component of production cost after raw material.
The activation process is done by using steam at high temperature of 800 – 1,100 °C, to make a food grade activated carbon the process must be done without using additional chemical substances.
Wood Activated Carbon
Wood Activated Carbon is an alternative of activated carbon for a specific uses. The raw material must be selected and then processed at low temperatures (200-300°C) to remove natural volatile components and residual moisture levels. This is the initial carbonization step. This is followed by activation process in high temperature (800-1100°C) in the presence of a stringently controlled flow of steam, which is used as the oxidizing medium. To make a food grade activated carbon the process must be done without using additional chemical substances.
Because of its special characteristic of surface area and pore structures, the wood activated carbon has ability to adsorb specific chemical matters in liquid or in gas phase. Because of its lower specific gravity it could be used for a special application, which needs lighter adsorbent.
Charcoal usually made by coconut shell or mixed wood. It must be made by selective materials that Indonesia archipelagos have many sources. The high quality of charcoal could not produced by a short time firing process, to find a high quality is needed enough time in firing.
The raw material of Coconut Shell is fired at temperature 300 – 500°C, and the raw materials of mixed wood are fired at low temperatures 200-300°C. The firing (carbonation) process is done in absence air, to remove natural volatile components and residual moisture levels, also to release moisture & volatile content as well as to make initial pore structure of carbonaceous material. Impurities in coconuts shell charcoal are removed by screening physical processes. To make a food grade activated carbon the process must be done without using additional chemical substances.