Silica gel is a kind of highly active adsorption material. It is usually formulated by sodium silicate and sulphuric acid reaction and through a series of aftertreatment processes such as aging, pickling, etc. Silica gel is a morphous substsnce. Its chemical molecular formula is mSiO2.nH2O. It is insoluble in water and any other solvent. It is nontoxic, nonodor and chemically stable .Except for alkali and hydrofluoric acid, it does not react with any other substance. Owing to their different manufacturing methods, the various types of silica gels are formulated with different pore structures. Thanks to its unique chemical composition and physical structure, silica gel possesses a number of characteristics with which other similar materials are incomparable, such as high adsorption feature, stable thermal performance, stable physical property and relatively high mechanical strength, etc.
According to the different pore diameters of silica gels, they are categorized into large pore silica gel. Owing to their different pore structures, their adsorptive humidity, macro-pored silica gel has a relatively high adsorption capacity.Whereas, under the circumstance where there is a low relative humidity, fine-pored silica gel has a higher adsorption capacity than macro-pored silica gel. The pore structurd of silica gel Type B lies between macro-pored and fine-pored silica gel, so its adsorption amount is also between those of macro-pored and fine-pored silica gel. Large pored silica gel is usually used as catalyst carrier, matting agent and toothpaste abrasive, etc. Therefore, the appropriate type is to be selected according to your specific field of application.
Safety Performance
The main component of silica gel is silica, which is chemically stable and flame-resisting.Silica gel is a kind of non-crystalline silica. The dust content inside the workshop should be controlled to be no more than 10mg/m3. The workshop shall be well-ventilated. Operators should wear mouth-muffles when processing.
The strong adsorption capability of silica gel may cause drying effects on human skins. Therefore,operators should be instructed to wear working clothes when processing. If silica gel accidentally comes into one's eyes, be sure to wash them using a large amount of water and seek for medical care as soon as possible.
Containing small amount of cobalt chloride and being toxic, blue silica gel should be kept from cobtacting the foods and inhaling into one's mouth. Seek for medical care as soon as possible once there is a poisoning accident.
Storage and Packing
Silica gel is strong in moisture absorption, therefore, it should be stored in dry places. Shelf racks should be put between the container and the floor. The containers are steel drums, paper bags, cardboard boxes, plastic bottles, polyethylene plastic compound bags and flexible container bags,etc. Please refer to the categorized product descriptions for detailed packing specifications.
The products should be kept from rain、moisture、sunlight.
The Reclamation of Silica Gel
Since silica gel adsorbs steams and other organic substances from the media, its adsorption capability declines. After being reclaimed, it can be used again.
(1).The reclaim of silica gel after steam adsorption
After adsorbing moistures, the moistures contained in silica gel can be removed by heating deadsorption. There are many methods for heating, for example, by electrically heated stove, remaining heat in the flus and hot air drying, etc.
For heating dradsprption, The temperature should be controlled to be within the range of 120-180℃.Forblue gel indicator, chromotropic silica gel and blue silica gel DL, the temperature should be controlled to be within 100-120℃.
When reclaiming industrial silica gels, make sure the highest temperatures are within the following limits:
Macro-pored silica gel no more than 600℃
Fine-pored silica gel no more than 200℃
Blue gel indicator (or chromotropic silica gel) no more than 120℃
Silica alumina gel no more than 350℃
The reclaimed silica gel can be put into use again as long as its moisture content is controlled to be less than 2%.
2).The reclamation after organic impurities adsorption
Roasting
Put macro-pored silica gel into a roaster and gradually rise its temperature to 500-6℃.After about 6-8 hours,the gel grains become white or yellowish-brown.For fine-pored silica gel, the roasting temperature shall be not more than 200℃.
Bleaching
Put silica gel into saturated steam to adsorb until it is fully saturated, then drop it into hot water to soak and bleach. Detergent can also be used to remove the waste oil and other organic impurities.After washing it in clean water,dry it to remove the moistures.
Solvent Rinsing
Depending on the organic substances adsorbed by silica gel, select the appropriate solvent to dissolve the organic substances adsorbed inside silica gel, then heat up silica gel to get rid of the solvent.
(3).Points for Attention in Silica Gel Reclamation
Gradually rise up the temperature in drying reclaim to prevent the gel grains from exploding and thereby from reducing the recovery ratio as a result of severe drying.
In roasting reclaim, excessively high temperature may cause changes to the pore structure of silica gel, thereby substantially reducing its adsorption effect and affecting its usefulness.
For blue gel indicator or discoloring silica gel, the temperature for deadsorption reclaim shall be not more than 120℃, otherwise, its developing agent will be gradually oxidized and therefore lose its devdloping effect.
3. The reclaimed silica gel shall usually be sifted out to get rid of the fine grains, thus making the grains well-distributed and uniform. |
