Abstract
Sensor-based sorting was developed and is extensively used in the waste recycling environment. The mining industry adopted and optimized the sorting and separation of one material from another. Robben, C. and Wotruba, H., 2019 noted that around 2005 the diamond mining industry adopted pneumatic ejection for separation of diamonds from kimberlite and alluvial material. The detection and characterisation of material is well understood. Concepts such X-ray fluorescence (XRF), Ultraviolet (UV) and magnetism are utilized. The mechanical ejection or removal of particles is fairly underdeveloped. Very little research in this area is published for public consumption, this is because most of the research outcomes are used for competitive advantage purposes.
This research set out to understand the behaviour of pneumatic ejection nozzles under ideal and imperfect conditions. The study also set out to determine the impact of these conditions on the ejection efficiency of an automated sorter. The study found that ejection systems are often operated in environments that are not suitable for efficient ejection. For ideal conditions, a kinematic analysis of the ejection forces required to move a particle to the intended area was conducted. The contamination of ejector nozzles (caused by foreign material) can cause a 40% reduction in blast strength. This leads to inefficient separation and in some cases loss of valuable material. in a diamond mining environment where high value stones command prices of up to R250 million rand, this loss can be significant.
The research analysed various concepts and solutions that can prevent or minimize the impact of contamination on ejection sorting efficiency. One-way valves that allow air to flow in one direction and then close afterwards were utilized for this purpose. Although one-way valves cause a reduction in blast strength, various levers such as increasing the incoming air and increasing/decreasing the nozzle open time can be utilized to overcome this disadvantage. Using Matlab and high-speed image capturing, the behaviour of ejected particles under ideal and imperfect conditions was analysed. This allowed for a better understanding of the behaviour of the particle after ejection.