hpgr

High-pressure grinding rolls(HPGR) have been widely used in the mineral crushing industry due to their energy efficiency and improved mineral liberation. This research examined the effect of HPGR and traditional crushing methods on low-grade iron ores' breakage and selection functions. The breakage function was calculated using Bẻrubẻ, Herbest & Fuerstenau, and Modified Herbst & Fuerstenau methods, and it was observed that HPGR increases the breakage function (Bi1) for most size fractions, resulting in higher percentages of finer particles after grinding compared to traditional crushing methods. However, this difference diminishes as the particle size decreases. The selection function analysis showed that HPGR increased particle breakage rate compared to traditional methods. Moreover, the selection function of the samples peaked at -1.410+1.680 mm before declining, suggesting that the highest breakage rate occurred at this size. The Broadbent-Calcut method also revealed that the value of Φ varied for different sizes, indicating a non-normalized breakage function. Additionally, the value of γ for HPGR-crushed samples was lower than traditional methods, indicating that HPGR produced finer particles.

The present study aims to evaluate the effects of fracture mechanism on physical parameters such as size, shape, and specific surface area and to provide a description on how the grinding mechanisms of ball mill and High-Pressure Grinding Roll (HPRG) work. Moreover, the effects of these parameters on qualitative indicators of green pellets were also investigated. Furthermore, the amount of fine particle and surface shape of the obtained particles were compared. Results showed that the specific surface area of particles produced through HPGR is more than Ball Mill. This feature was recognized as the result of the increasing fine particles in the range of 7-25 µm and the presence of micro and macro cracks and fractures on the surface of the most particles manufactured by HPGR. In addition, pelletizing processes of HPGR and ball mill products at the same particle size distribution of 80% less than 43 and 90 µm showed that green pellets produced with HPGR product in d80=90 µm have more drop number and compressive strength in both dry (D.C.S) and wet (W.C.S) modes compared to ball mill. Also, the green pellets produced from HPGR product at d80=43 µm had higher drop number and W.C.S than ball mill product. But, compressive strength of green pellets in HPGR product showed 63.18% lower values of D.C.S than pellets produced by ball mill product at d80=43 µm. The reason for the lower D.C.S of the HPGR product is the increase of fine particles and specific surface area that consequently led to high water absorption by the fine particles.

Summary :The dominant mechanism in the High Pressure Grinding Rolls (HPGR) is compressive breakage. A laboratory scale experiment could be implemented to study the compressive mechanism. In the present research, for the first time in Iran, the piston and die device consists of controllable hydraulic press (P&D test) were utilized at Golgohar complex to study the compression breakage. This test was applied to investigate the edge recycle effect on the HPGR performance.
The usage of HPGR in the iron mineral processing plants is extending in Iran. Edge product of the HPGR is coarser than the central product that is not favorable for downstream processes. It is imaginable that the HPGR performance could be controlled by separating and circulating the edge materials. Before any mechanical changes in the industrial HPGR machine at the 4th train of iron concentrate plant in Golgohar, it was necessary to investigate the edge recycle effect fundamentally. From operational point of view, the HPGR in pilot scale is required for feasibility study, investigating the variables and predicting the associated operational advantages of any changes. The pilot plant scale of HPGR is not available at Golgohar complex. Also, conducting the pilot scale experiment requires a significant amount of samples, which is costly and time-consuming.
In both cases, fundamental and operational researches, the simple, available and knowledge-based laboratory tests are required. In addition, the laboratory tests play an important role in understanding and prediction of variable behaviors in industrial scales.
Methodology and Approaches : A laboratory method was developed to study the effect of the edge product recycling. After designing and constructing of the piston and die system, compressive breakage tests were conducted at the pressure of 1730 bars using samples taken from the feed of the 4th train of the concentrate plant. For separating the central product from the edge product of the experiments, a punch system was designed and constructed. To obtain the effect of edge product circulation, this material was mixed with the fresh feed at the ratio of 0.8. The sample was compressed at the same pressure. The D50 of the product was reduced by 25% with the edge product recycle. Particles from test product were studied using optic microscope and scanning electron microscope (SEM). Also a numerical method (trapezoid formula) was implemented to calculate the compressive breakage specific energy.
Results and Study of piston and die test cake product particles using optic microscope and scanning electron microscope (SEM) showed that just a few numbers of particles have surface micro cracks. Therefore, circulating the edge product will increase probability of particle breakage or crack creation. Finally a flowsheet was proposed which allows circulating the edge product of the industrial HPGR at the 4th train of the concentrate production of the Golgohar complex.
Also the compressive breakage specific energy was obtained by a numerical method named trapezoid formula using force-displacement graph. This graph was attained from piston and die test data.