Dust in Mineral Processing

The generation of airborne dust is a significant problem for the mineral industry. Previous studies in the literat-ure concluded that surfactants were the most effective dust suppressant agents since they enhance the wetting characteristics of the material. However, personnel in the iron ore industry have reported that these agents were not effective. Why is it that surfactants are effective for materials like coal but not iron ore? If surfactants can not control dust levels, what other reagents should be considered

Novel Binders and Methods for Agglomeration of Ore

Many metal extraction operations, such as leaching of copper, leaching of precious metals, and reduction of metal oxides to metal in high-temperature furnaces, require agglomeration of ore to ensure that reactive liquids or gases are evenly distributed throughout the ore being processed. Agglomeration of ore into coarse, porous masses achieves this even distribution of fluids by preventing fine particles from migrating and clogging the spaces and channels between the larger ore particles. Binders are critically necessary to produce agglomerates that will not break down during processing. However, for many important metal extraction processes there are no binders known that will work satisfactorily. A primary example of this is copper heap leaching, where there are no binders that will work in the acidic environment encountered in this process. As a result, operators of acidic heap-leach facilities see a large loss of process efficiency due to their inability to take advantage of agglomeration. The large quantities of ore that must be handled in metal extraction processes also means that the binder must be inexpensive and useful at low dosages to be economical. The acid-resistant binders and agglomeration procedures developed in this project will also be adapted for use in improving the energy efficiency and performance of other agglomeration applications, particularly advanced primary ironmaking

NOVEL BINDERS AND METHODS FOR AGGLOMERATION OF ORE

Many metal extraction operations, such as leaching of copper, leaching of precious metals, and reduction of metal oxides to metal in high-temperature furnaces, require agglomeration of ore to ensure that reactive liquids or gases are evenly distributed throughout the ore being processed. Agglomeration of ore into coarse, porous masses achieves this even distribution of fluids by preventing fine particles from migrating and clogging the spaces and channels between the larger ore particles. Binders are critically necessary to produce agglomerates that will not breakdown during processing. However, for many important metal extraction processes there are no binders known that will work satisfactorily. Primary examples of this are copper heap leaching, where there are no binders that will work in the acidic environment encountered in this process. As a result, operators of many facilities see large loss of process efficiency due to their inability to take advantage of agglomeration. The large quantities of ore that must be handled in metal extraction processes also means that the binder must be inexpensive and useful at low dosages to be economical. The acid-resistant binders and agglomeration procedures developed in this project will also be adapted for use in improving the energy efficiency and performance of a broad range of mineral agglomeration applications, particularly heap leaching

Optimization of Comminution Circuit Throughput and Product Size Distribution by Simulation and Control

The goal of this project is to improve energy efficiency of industrial crushing and grinding operations (comminution). Mathematical models of the comminution process are being used to study methods for optimizing the product size distribution, so that the amount of excessively fine material produced can be minimized. This will save energy by reducing the amount of material that is ground below the target size, and will also reduce the quantity of materials wasted as slimes that are too fine to be useful. This will be accomplished by: (1) modeling alternative circuit arrangements to determine methods for minimizing overgrinding, and (2) determining whether new technologies, such as high-pressure roll crushing, can be used to alter particle breakage behavior to minimize fines production. In the sixth quarter of this project, work was centered on analyzing the considerable plant data gathered during the first year of the project. Modeling is being carried out of the hydrocyclone portion of the grinding circuit, since this has been identified as the primary source of overgrinding and inefficiency

Optimization of Comminution Circuit Throughput and Product Size Distribution by Simulation and Control

The goal of this project is to improve energy efficiency of industrial crushing and grinding operations (comminution). Mathematical models of the comminution process are being used to study methods for optimizing the product size distribution, so that the amount of excessively fine material produced can be minimized. The goal is to save energy by reducing the amount of material that is ground below the target size, while simultaneously reducing the quantity of materials wasted as ''slimes'' that are too fine to be useful. This is being accomplished by mathematical modeling of the grinding circuits to determine how to correct this problem. The approaches taken included (1) Modeling of the circuit to determine process bottlenecks that restrict flow rates in one area while forcing other parts of the circuit to overgrind the material; (2) Modeling of hydrocyclones to determine the mechanisms responsible for retaining fine, high-density particles in the circuit until they are overground, and improving existing models to accurately account for this behavior; and (3) Evaluation of advanced technologies to improve comminution efficiency and produce sharper product size distributions with less overgrinding

Application of surface chemical fundamentals to improving industrial filtration rates

The throughput of any process is limited by the step with the lowest throughput. In iron ore processing, filtration is used to dewater the iron ore concentrate created during reverse flotation. The conditions of the reverse flotation of iron ore and the efficient filtration of iron ore concentrate are found to be at odds with each other. We show that optimizing the filtration conditions should reduce cation retention in the filter cake, which also improves pellet quality in laboratory scale work. Experimental work was performed to investigate potential implementations at plant scale. Based on data collected at operating magnetite concentrators, it has been found that adding CO2 into the filter slurry can increase filtration rates dramatically. In plant scale work, filtration rates were increased by up to 23.7% with the addition of 0.54kg of CO2/ton of feed. We compare these results with laboratory scale results on the same process and elaborate on the theory leading to this discovery, while considering its potential impact on final pellet and iron product quality

On-Line Viscometry in Particulate Processing

On-line viscometry of suspensions is very difficult compared to viscometry of pure liquids. The problem arises because of the unstable nature of the suspensions, particularly when coarse and fast settling particulates are present. Several attempts have been made in the past in which special mixing chambers have been designed to maintain slurry homogeneity while measuring viscosity. However, the credibility of these instruments are questioned by many authors, as quite often the same systems measure different Theological behavior for similar suspensions. In most of the designs suggested in the past, solving one of the problems of suspension viscometry introduces new problems. For example, agitation can keep the solids suspended, but it can also seriously affect the sensitivity of the viscometer. In this article the problems involved with three different types of viscometers (rotational, capillary, and vibrational), which have been used for measuring viscosity of suspensions, are discussed. © 1995, Taylor & Francis Group, LLC. All rights reserved

Determination of Changes in Rheological Properties of Coal Slurries in Process Streams

A new technique involving a rotational (coaxial cylinder) viscometer and a vibrating sphere viscometer was developed for the rheological characterization of coal slurry process streams as either Newtonian or non- Newtonian. Both viscometers were able to measure apparent viscosity as low as one centipoise, and special precautions were taken to allow measurement of rapidly settling coal suspensions. In this technique, the vibrating sphere viscometer was used to measure the apparent viscosity at a high shear rate, while the rotational viscometer was used to measure the apparent viscosity at a low shear rate. Together, the two instruments could determine the shear-rate dependency of the viscosity, and thus provide an estimate of the total slurry rheology. The technique was first verified using two types of fluid with known rheological properties; sucrose solutions ranging from 10 to 60% by weight (Newtonian fluids), and solutions of Dow Methocel A4M ranging from 0.5 to 2% by weight (Pseudoplastic fluids). Following verification with the known fluids, a high-ash Pittsburgh seam bituminous coal was ground to 80% passing 34 micrometers, and was used to prepare slurries ranging from 10 to 45% solids by weight in distilled water. Apparent viscosity of each slurry sample was measured simultaneously by both viscometers and the results were then compared. With this technique, the onset of non- Newtonian flow behavior was clearly observed for slurries of this particular coal when the solids loading exceeded 20% solids by weight. © 1995, Taylor & Francis Group, LLC. All rights reserved