Waste treatment of ornamental rocks

This work has as objective or study the re-approval of metallic part and the characterization of oxides present in the granite residue generated in the unfolding stage. For this, were used: magnetic separator, concentrating table and cyclone. After the recovery tests, the product can be used in tests with a higher content of metallic Fe that was taken for the production of briquettes.

Ornamental rock is defined as a natural rock material, submitted to different degrees of improvement (smooth, molded, polished and cut) and used to perform an aesthetic function.

The processing of ornamental rocks involves several stages. The extraction of rocks in the open sky for transformation into blocks is the first of these steps. The second stage is where the blocks unfold or unfold, that is, the blocks are transformed into layers that can have different thicknesses. This stage is also known for its primary benefit (the waste generated in this stage that has been studied). The final stage of processing is the transformation of the plates into the final product, where equipment called polishing machines are used. It is in this stage that polishing, animation, cutting and final finishing of the covers are carried out. An important fact is that the exploration of ornamental rocks, from extraction to finishing, generates an average amount of 40 to 50% of waste.

In the unfolding process (primary processing) the main methods of obtaining the plates are by cutting with blades, diamond disc or diamond wire. In these cutting processes, 25 to 30% of the block ends up becoming waste. This residue consists of water, lime, steel shot and crushed rock. The residues are generally stored in open air places or in some cases, are thrown into rivers without any type of treatment causing silting problems, contaminating river and stream waters and even contaminating natural water reservoirs. Initially, the chemical and physical characterization of the waste was made through chemical analysis, X-ray diffraction, scanning electron microscopy and granulometric analysis.

After characterizing the residue, the processes for the recovery of metallic Fe were initiated, which involved: magnetic separation, concentrating table and cyclonage. The magnetic separation was carried out in three stages: the first, where a high intensity magnetic wet separator was used, where only the remaining magnetic field of the equipment was used. In the second stage, where the magnetic material obtained in the first stage was subjected to a new manual magnetic separation using a rare earth magnet. In the third stage, the magnetic material obtained with the rare earth magnet was subjected to manual magnetic separation with a ferritic magnet.

In the tests of the concentrating table, variations were made in the inclination of the table, frequency of oscillation and flow of washing water. In the cyclone tests, the varied parameter was the supply pressure. Variations were made in the equipment parameters in order to improve and define the best parameters for the recovery of metallic Fe. After each test, volumetric chemical analysis was performed to determine the metallic Fe content obtained in each product. Due to the results obtained, the magnetic separation method was the one that presented the best results, making it possible to obtain a ferrous concentrate with 93% metallic Fe and a granitic concentrate with 0.6% metallic Fe. In the concentration table tests, the best result was a ferrous concentrate with only 13.7% metallic Fe, and in the cyclone tests it was possible to obtain a product with only 7.2% metallic Fe.

From the ferrous and granitic concentrate obtained in the magnetic separation, the characterization was performed through scanning electron microscopy, X-ray diffraction and granulometric analysis. From the obtained ferrous concentrate, briquettes were produced using 2% hydrated lime as a binder. Green and dry mechanical strength tests were performed on the briquettes produced. A mechanical resistance in green of a maximum of 1.02 kN was obtained and a dry resistance of a maximum of 3.59 kN.