You can perform a powder X ray diffraction. Each of these phase has a particular XRD pattern.

Inductively coupled plasma optical emission spectroscopy ICP-OES could help by giving you the ratio of silicon to aluminum. XRD would give you structural information about the product resulting from your extraction method, but I don't know whether your extraction method retains the original structure in the fly ash.

Also XRD will show only crystalline phases, non-crystalline alumino-silicate wont be visible. ICP will allow elemental compositions to be determined. or XRF or EDX.

No it is not exactly that you geting as a quartz form, the silica is entirely different from alpha glassy and quatz form. Somebody extract silica from fly ash and rice husk which was treated by alkaline method has entrily different physical property that of commercially obtained one. The extracted silica suppose you subject in XRD it shows just only amorphous region and very difficult to assign for silica. better go the simple EDS may indicate whether it has silica or not. or elese that extracted silica that you prepared silicalite material that may showed in XRD patterns. in hydrothermal process condition only change to glassy, quarts and mordinites and hope not available by direct extracted one. The physical identification of silica freely soluable in HF.

Good Mr. Manish i also want to know about how to quantified the amount of Quartz from direct extraction. If you posted that method it will be benifit by many of them rather than personal mail contact.

As the aluminium is also soluble in caustics like NaOH you have to check also for the aluminium content to be sure you have only extracted SiO2.

The first step would be to expose the sample to high temperature to "burn off" any "organic" matter. This oxidizes most if not all carbon compounds leaving mostly inorganic compounds. Then treat the sample with aluminum at high pH > 9. Of course, you have to keep track of the amounts of reagents added, but in general any aluminum oxides will dissolve at pH>9 since aluminum is amphoteric -- soluble at both high and low values of pH -- that is, pH > ~ 8.5 and pH< ~5.0. This provides a separation based upon base/acid values of pH. In all cases based upon pH, use KOH (not NaOH). The reagent NaOH reacts readily with atmospheric CO2 which will distort the result.

This separation, based pH solubility, and organic matter, leaves only a few

alternatives. This result can be checked using an addition of "pure" SiO2 (quartz), which is insoluble in both acid and base. This method does require using some internal

checks. However, it is not require instrumental controls, e.g. x-ray diffraction, which adds other experimental problems, and is difficult to carry out if the level(s) of quartz is low.

Vince Calder

As Hitoshi Masui, Hari Haran said, after alkaline extraction, your extract is no longer in its original form. The original crystal structural information is lost once it was dissolved. You may still be able to determine structure of any undissolved residue (if there is any structure) with XRF. However, even that depends on how rapidly the silicate particulate in the ash cooled. When one melts high purity quartz, it generally cools too rapidly to crystallize. Instead, it forms a glassy amorphous solid. Only if it cooled slowly will it form a crystalline structure. This may be the case. I don't know, since I don't know how rapidly it cooled or what effect other components of the particulate may have had.

The elemental determination is silicon, not silica. Silica is silicon dioxide or quartz. there are various crystaline structures which can all be classed as Silica. Crystal structure needs to be determined on the original sample material not on an extract. When you are extracting the silica you are dissolving the compound silica and creating an ionic form of silicon. The silicon in solution may still be a compund radical like a silicate but it is no longer a crystal form of silica until you precipitate it. It then hasa crystal structure that is generally not the form that was in the original sample. Crystal structure is best defined by Xray Diffraction. As others have noted, there may be various pretreatments of the original sample that are used to remove other material to improve the diffraction analysis. If you are trying to remove organic material, it was suggested that a high temperature be used. This is correct but depending on what you have decided is a high temperature, you can change the crystal form. Many crystal forms have bound water in the crystal and this is released at varying temperatures depending on the chemical makeup. Ideally you would do a low temperature plasma ashing to retain water of cyrstallization. Without that equipment, you would do an as received sample that has been dried at 110C until a constant weight is reached ( or typically two hours) and then do an XRD determination. Then you could follow that with a 250C ashing with good air circulation (ASTM publishes methods for coal analysis and has specific conditions for ashing that allow your results to be compared with other analysts). US National Bureau of standards also has coal standards that can be tested with your samples to show how a method is working. If you need to separate the silicon compound from other materials in the the sample, then you need to look at the process that generated the fly ash as well as the original material fed into the burner. If the coal has been ashed as per ASTM and the XRD carried out, you have a good idea of the form of silicon that is present at the start of the burning process. Then a literature search will provide you with information on how that original form will change with temperature. Generally alkali metals are present as are aluminosilicates and at furnace temperatures, they will tend to fuse together and form glassy aluminosilicates. AS others have stated, these tend to be amorphous and show no strong crystalline structure in XRD. That is still a useful XRD analysis as it show that the silicon is in a glassy state and with other elemental analysis or SEM/EDAX you will determne the silicate composition. If yhou are only trying to determine free silica for environmental health concerns, then a 250C ashing with air flow in the ashing furnace will remove the organic material and not shange free silica structure. You can do a 25% HCL extraction and not lose a lot of the free silica but will remove some of the other soluble metals. XRD will then provide you with a good indication of the free silica.

Yah i agree with your fly ash system treatment to comparision, but i feel it not that much problem so called silica (SiO2) which tetra hedra involved in alumino silicates. Ex glassy silica it has structred involved in silicon. As you recommended EDX is know to conform whether it presence silica or not, but still doubting direct extracting material subjected to XRD for Silica conformation. It is to be secondary, that we are grown up other structure to conform in XRD, what would we have direct analysis suppose to be a given compound is presence of silica or not. The statement also considered one about glassy aluminosilicalite, its not a silicalite its a zeolite.

I may not know what is the structure of free silica obtained from XRD, but i synthesized silicalite-1 which has involved tetrahedral coordination of silica. If it i dissolved in 25 % of HNO3 may i get colasped structure, but expected it may be the amorphous form.

Mr. Richered raising intreasting question rapid cooling avoid glassy form for pure crystalline nature. While rapid cooling (quenching) nutrients in the gel solution which fast rate heat of enthaphy released that make make more tetrahedra bonding for high crystallinity. Thats why we do quenching.

http://www.hindawi.com/journals/jnm/2012/528174/ discusses fly ash and different silica forms. The research group might be able to provide more analytical information

You may try it by treating to heavy liquid like ZnCl2. Then check for type later.

crystal structure is determined by X-ray diffraction pattern. also semi quantitative analysis is possible with X-ray diffractometry.

I am not sure how silca was separated from the solution after dissolution in NaOH. Usually NaOH extration followed by an acid precipitation gives amorphous solid with some impurities. XRD analysis will tell whetheryou have amorphous or quartz form. It may also show any impurities present. For quantitative assesment of impurities XRF (EDX) will be a quick method.

In Manish's procedure the NaOH did not fuse with the Quartz but would with other silicates. When water washing on filter paper all the soluble materials are gone including silicates and any quartz that was present remains on/in the filter paper. The paper is ashed leaving quartz and any other insoluble material. This residue is weighed and the HF added to fume off the quartz. The sulphuric is added as a high boiling acid to drive of off the HF. Finally on drying and weighing the weight loss is due to the quartz which was present.

SEM analysis shows the association of the silicon. This analysis is done on the original sample without exctraction. As siad before: why do you want to the form of the silicon

As an example of SEM analysis of flyash to analyse its form:

Silica fines from included quartz in pulverized-coal combustion

HM ten Brink, S Eenkhoorn, G Hamburg

Fuel Processing Technology, 1997

Thanks to everyone for their valuable comments and suggestions. I will get back to this topic with few of my results and further difficulties if any...

can silica and aluminium be extracted on commercial basis as a small scale industry in India , as flyash is available in abundance . If so, can anyone suggest me the right feasible process for class C as well as class F flyashes