Prediction of the Edge Recycle Effect on the High Pressure Grinding Rolls Performance Using Piston and Die Test

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.
Introduction
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 4^th 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 4^th 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 Conclusions
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 4^th 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.