DENSITY IN THE FLOTATION PROCESS WHITEPAPER INTRODUCTION THE FROTH FLOTATION PROCESS Are you looking for a higher recovery rate in In previous process stages fine particles the Flotation process by means of were created and valuable minerals were automation and instrumentation? This released from their carriers, also called the whitepaper describes the purposes and gangue. In general, flotation is used to benefits of measuring density at different separate and recover. The valuables are applications in froth flotation. First, the concentrated and separated from the unwanted particles (gangue). This is done froth flotation process itself and control using chemicals and froth. Basically, this purposes are explained, then five key process exploits differences in surface reasons for measuring density will be given. properties between minerals and gangues. A full optimization for a maximum recovery The froth flotation principle is a complex in the flotation process can only be combination of the laws of surface achieved when a novel of instruments and chemistry, crystallography and physics. The analyzers are used together, such as density process efficiency depends on aspects such as density, electrical conductivity and gauges, level gauges, flow meters, froth physical and chemical properties. cameras, etc. This whitepaper will show the importance of the Density meter, which is Without a flotation process, many metals Rhosonics’ area of expertise. and inorganic raw materials would be extremely scarce and expensive, as there are currently not many high-grade deposits that could be processed by simple physical and mechanical methods. Addition of chemicals Mass flow meter Air addition supply Mass flow meter pH sensor Froth Feed slurry Ultrasonic Slurry Density Meter (SDM) Underflow Figure 1: The flotation cell overview of measuring applications ©RHOSONICS ∙ WHITEPAPER ∙ FIVE REASONS FOR MEASURING DENSITY IN THE FLOTATION PROCESS ∙ 06/2020 ∙ WWW.RHOSONICS.COM PURPOSE OF PROCESS CONTROL WHY DENSITY MEASUREMENT? The main objectives when controlling the Instruments, such as density meters help flotation process is to maximize the recovery operators to efficiently monitor and control and boost the metallurgical performance. the flotation process, optimize it and An enriched product is created by decreasing prevent process failures. the amount of gangue. When used together with an advanced To achieve these objectives the slurry control system, density readings allow to needs to be continuously monitored and automatically control valves, pumps and controlled, allowing process stabilization have an efficient chemical or air dosing, and ensuring optimal flotation conditions. resulting in the improvement of the process that can lead to a higher enrichment and MEASURING POINTS recovery of valuable materials. In the flotation cell, there are several There are multiple reasons for measuring possible installation points for density density in the flotation process, which meters. For example in the feed slurry, could differ per application. The following underflow of the cells and final concentrate. five topics are highlighting the main reasons Please check the overview of measuring for measuring density. points in figure 1. Released particles Binary composites Ternary composites Gangue Valuable 1 Valuable 2 Figure 2: The flotation cell needs to separate the valuable materials from the gangue ©RHOSONICS ∙ WHITEPAPER ∙ FIVE REASONS FOR MEASURING DENSITY IN THE FLOTATION PROCESS ∙ 06/2020 ∙ WWW.RHOSONICS.COM 1: OPTIMUM FEED DENSITY middle size particles consist of minerals and gangue. The gangue can only be separated Density measurement in the flotation feed from the valuable minerals in the flotation is a known installation point in mineral cells when the particles were grinded fine processing. The percentage of solids in the enough in previous stages. feed is important for optimal operation of the flotation cell. Also, a combination of a density meter and a flow meter in the flotation feed and line of the final product of the flotation, allow to calculate the performance of the circuit. The optimal pulp density in the feed of the flotation process depends on the type of ore, due to different characteristics such as specific gravity and shape of the particles. For example, silicate minerals respond best Figure 3: The bubbles remove the fine particles to the flotation process at a feed density of approx. 20 to 30 % solids and the optimal Real-time density measurement can help to coal pulp density varies in practice from 6 verify changes in the slurry from the to 25 % solids (Yarar & Dogan, 1984). grinding circuit to the flotation cells. The Additional research should be done to slurry density has a high correlation with determine the optimum feed for a particle size, therefore the operator could particular operation. use this parameter (together with other The effect of flotation feed density on variables) to improve the control over the metallurgical performance has been process. investigated. Results of test work have shown that the pulp density affects key 3: EFFICIENT ENRICHMENT parameters of the flotation process in both Optimal flotation means reducing the the pulp and froth phases (Runge et al., amount of gangue that is sent together with 2012). One of the findings was that froth phase recovery presumably improves valuable minerals to further stages of the because of a stabilising effect due to a process. An enriched product should be greater loading of solids on bubble produced with the lowest energy costs, surfaces. containing most valuable materials (the concentrate). Decreasing the amount of 2: PREVENT MIDDLINGS gangue can improve the quality of the concentrate. Particle size plays a crucial role for the enrichment of ore in the flotation process. Instrumentation plays a crucial role in this The flotation operator wants to prevent enrichment process, because it is the base middling’s (product which is neither clean for all process control. Automation can lead mineral product nor reject/tailings). These to a high level of performance in the circuit. ©RHOSONICS ∙ WHITEPAPER ∙ FIVE REASONS FOR MEASURING DENSITY IN THE FLOTATION PROCESS ∙ 06/2020 ∙ WWW.RHOSONICS.COM Besides density, the air injection and dosing of reagents should be monitored and controlled for efficient product enrichment. Smart air injection could solve problems with froth levels without using too much reagents. The correct choice of instrumentation can only be achieved if a detailed understanding of the operation and application of the required instrument is acquired within a Figure 5: Advanced flotation cell process control given process (Laurila et al., 2002). 4: FALLING SLURRY LEVEL The pulp level inside the cell can fall due to an increase of ore feeding (XinHai, 2020). In Optimization this case, the flotation operator should Maximize the beneficiation decrease the feed density, adjust grinding and classifying processes or adjust the Advanced control reagent dosing or air injection to keep the Reject disturbances, control slurry level at a certain point. An in-line Base level control density meter can be used to check in real- Control froth level, aeration time the amount of ore in the feed (XinHai, rate and dosing of reagents 2020). Instrumentation Valves, sensors, level gauges, density meters Figure 4: Hierarchy in the flotation control system (Laurila et al., 2002) Installing sensors is important, but the sensor itself will not guarantee continued performances. Having a skilled team is also essential. The flotation operator should be Figure 6: Flotation cells at a Moroccan processing capable of interpreting and understanding plant the measurement data. The operator is 5: ORE PILES UP IN THE TANK critical in order to make the most out of the collected process data. Advanced process Another problem is that the ore in the control is needed to support the operator flotation tank piles up (XinHai, 2020), this and to achieve good performances in the could have been caused by a too high feed entire flotation circuit (Di Sandro, 2017). slurry solid content, which can be monitored in real-time by the use of a density meter. ©RHOSONICS ∙ WHITEPAPER ∙ FIVE REASONS FOR MEASURING DENSITY IN THE FLOTATION PROCESS ∙ 06/2020 ∙ WWW.RHOSONICS.COM Other reasons could be changes in pressure, CONCLUSION a high inflating volume and changes in the suction capacity of the suction tank. The As discussed in this whitepaper, measuring flotation operator can use different tools to density in the flotation circuit is important. make the slurry flow again. Density measurement can be used for advanced process control, preventing AVAILABLE EQUIPMENT falling slurry levels and ore piling up in the tank, and to increase the efficiency and Density measurement is usually done by recovery in the flotation process. Together radiation-based measuring devices. This with flow measurement, the density can technology has been used in the mineral also be used for the mass balance, and to processing industry for decades. However, calculate the performance of the circuit. nowadays governmental regulations are getting stricter and associated costs are MORE INFORMATION? increasing. More nuclear density meters are being replaced by alternatives. These Rhosonics has more than ten years of alternatives can do the same job, without experience in using ultrasonic technology administration costs and health and safety for non-nuclear density measurement in risks related to the nuclear source. the mineral processing