X – RAY DIFFRACTION ANALYSIS OF SLUDGE AND DUST PRODUCED IN STEELWORKS

Before handling, storage, disposal, these wastes need to be analyzed. In many cases, it is not enough to know only their chemical composition, but it is necessary to determine their mineralogical composition, or to know exactly what is their crystallographic structure. This can be well done using X – ray diffraction device. Examples of sludge from Steelshop and Tin Mill, and dust from Sintering and Steelshop demonstrate current opportunities of X – ray diffraction. The analysis was done using programs of "search match" type with diffraction database PDF2 – 2004 and crystallographic COD database. Diffraction records were refined by Rietveld method in the TOPAS program.

cold steel rolling. This process is carried out in oxygen converter blowing technical pure oxygen or in electric arch furnace. Depending on dedusting system, various kinds of sludge and dust are formed which are recycled or stored by different ways. The whole process of production and processing of steel creates a lot of components such as sludge, dust, fly, ash, slag, deposit etc. These different multi-component materials are captured, stored and disposed using the complex techniques. The first step to waste disposal or regeneration is its knowledge. There are many methods used in this process, among which Xray diffraction has its legitimate place. This method can, in many cases, determine not only the chemical but also the mineralogical composition of the wastes. Exact knowledge of the crystal structures will assist us in disposing or further processing of waste generated in the production process. This is also applied in the production of steel, where a diverse amount of waste is generated in various technological processes. The analysis of these products is difficult and besides knowledge and experience it requires also the specific analytical instruments with powerful hardware and software. Analyzing all these materials is very difficult and long process. In further text we will limit the discussion to the Xray diffraction analysis of steelmaking sludge and different dust [8][9][10][11][12][13].

Experimental materials and methods 2.1 Experimental device
The Xray diffraction analysis of the investigated materials was done using versatile analytical device URD 3003PTS Seifert, which besides the phase analysis allows measurement of residual stress and texture of steel sheets. Wavelength can be changed by selecting the appropriate Xray tube -Mo, Cu, Co or Cr. For phase analysis the geometrical goniometer is arranged to bar focal point, and the rapid measurement is done using bar detector type Meteor1D. With this detector, the measurement takes about 15 to 20 minutes. Measured diffraction record is processed and evaluated using packages of programs of "search -match" type like DifracEVA with PDF2 -2004 and COD database, and programs refining the Rietveld method like AutoQuan and TOPAS. This powerful software enables to qualitatively and quantitatively refine each measured diffraction record [14][15][16].

Solution and experimental material
Samples measured by Xray diffraction method must be isotropic, therefore they are prepared in the form of fine powders. The optimum powder has particle size of about 10 microns. The powder is prepared using vibratory mill or alumina grinding mortar. Plant sludge and dust samples were prepared in a vibration mill. Milling time was approximately two minutes. To examine the sludge from Steel shop, two samples with different grain size were collected. Sample 1 was designated as gross (thick) sludge, and sample 2 was designated as a fine sludge. Results of the analysis are shown in Table 1. All diffraction records were refined by Rietveld method in the TOPAS program. The table shows that they have slightly different chemical and mineralogical composition, which is given by the place and time of sampling. The same applies for the quantitative composition, which is affected in some cases by portion of the amorphous component. These real heterogeneous multicompact oxide materials contain fine particles of iron, iron oxideswustite and magnetite, calcite, brownmillerite, and sample 2 also contains portlandite and a considerable amount of graphite. No hematite was found in samples. DOI   At this point, the Xray analysis could be completed, because the device is not able to detect very small amounts of substances, which may be found in the examined samples. Since the samples contain fine particles of iron and magnetite, they can be separated by the magnet, thereby increasing the portion of non-magnetic components in the samples. This can be done by small magnet wrapped in paper. Sample 3 was formed by separation of sample 1 and similarly sample 4 was formed by separation from sample 2. Xray diffraction analysis results are presented in Table 1. Manual separation failed to completely remove iron and magnetite particles, but their content was reduced. In the case of gross (thick) sludge it was reduced very significantly. Wustite content significantly increased in the sample 3. There were new crystal structures that emerged in the diffraction record, which could be found in the original records. In both samples were found lime, srebrodolskite, dolomite, periclase. In a sample 3 it was of diopside and in sample 4 hedenbergerite and franklinite. Refined diffraction record of gross (thick) Steelshop sludge after magnetic separation is shown in Fig. 1. Results of Xray diffraction analysis of the two dust samples are shown in Table 2. Analyzed was the Sintering dustsample 5, and Steelshop dustsample 6. Their chemical and mineralogical composition is different, which is consistent with the sampling point. Common minerals are iron oxides hematite and magnetite, silica, carbonates, limestone and dolomite, and small amount of baddeleyite. Nonmagnetic particles were manually separated from both samples using a small permanent magnet. Sample 7 was formed after separation of sample 5, and sample 8 was formed from sample 6. As shown in Table 2, manual magnetic separation in this case was not very successful. Probably cause is the high content of hematite and graphite. Fine particles of magnetite carry away also non-magnetic particles and the presence of hematite with graphite assists in that. In both cases there is increased content of calcite. method using TOPAS program. Fig. 2 and 3 show fitted refined record of Steelshop dust sample.

Fig. 3
Refined X-ray diffraction record of steel dust after manual magnetic separation

Conclusions
Samples of sludge from Steelshop and Tin Mill and samples of dust from Steelshop and Sintering were analyzed by X-ray diffraction method. All diffraction records were refined by Rietveld method using TOPAS program.  To achieve the best quality results, non-magnetic particles were separated from samples by simple manual way. This effect was strongly felt in the sludge samples, which contained iron and magnetite particles and where no hematite particles were detected. Magnetic particles could not be effectively separated from the dust samples with high portion of hematite.  The amorphous sample of sluge from the electrolyte of tinning linewas annealed in a furnace in order to crystallize. The oxide of tin cassiterite was identified in the sample.  Following minerals were found in the sludge samples with non-magnetic particles: lime, srebrodoskite, diopside, periclase, hedenbergite and franklinite, which were not found in the original samples.  Steelshop and Sintering dust commonly contain following minerals: hematite, magnetite, quartz, calcite and dolomite. Sintering dust differs from the Steelshop dust by small amount of lime and salts: sylvite and halite, which were found in the Steelshop dust. The Steelshop dust contains graphite, magnesite, hedenbergite and small amounts of fluorite, baddeyite and zincite.