Optics: measuring and testing – For light transmission or absorption – Of fluent material
Reexamination Certificate
2002-04-10
2004-04-27
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
For light transmission or absorption
Of fluent material
C209S168000, C348S091000
Reexamination Certificate
active
06727990
ABSTRACT:
GENERAL BACKGROUND OF THE INVENTION
The desired valuable minerals are separated from the ores in the mining industry by flotation. This is effected in flotation cells of continuous flow type, in which air is conducted into vigorously mixed slurry of ground ore and water. Due to chemical preprocessing, the grains of the valuable mineral tend to adhere selectively on surfaces of air bubbles, to be lifted with these from the slurry to the froth layer above its surface. At the same time, also other mineral grains and mixed (locked) grains of a weaker tendency to float rise to this layer, and return from froth to slurry takes place as well. The froth flows continuously over the cell edge down into a launder producing the concentrate of the cell.
The final concentrate of an industrial flotation circuit consists of concentrates of individual flotation cells, which usually have been cleaned by refloating them, often in several states. The content of the valuable mineral in the concentrate of the cell is, together with the recovery of the valuable mineral, the most important factor on which the economic value of its concentrate depends. Therefore the quality of the final concentrate and, at long intervals, also that of concentrates of the individual cells is controlled by taking samples and analyzing them in laboratory. The most important one of the instruments for immediate measurement of slurries in a flotation plant is the X-ray fluorescence analyzer which mostly analyzes metal contents of solids contained in sample streams separated from slurries. For its high price, this device however does not apply to analysis of the concentrate of a single cell, but instead of that analyzes joint samples of cell combinations or complete flotation circuits. The need for development of an instrument for on-line analysis of operation of single flotation cells or for that of material processed by them is therefore high. For this reason, an attention has recently been paid also to such measurements which relate to the flotation froth.
The appearance of the froth describes sensitively the operational state of the froth layer and even that of the whole cell, because all the material passing it and contained by it arrives to it through the slurry space of the cell. The surface of the froth is visible and the process controller traditionally inspects it by naked eye, in order to observe qualitatively its general outlook and specific features and to then base his manual control actions on his observations and conclusions. Thus he may describe the froth e.g. one of big bubbles, porridge-type, watery, dry, stiff etc., in addition to characterization of its color.
The quantitative, instrumental evaluation of the froth has become possible, as the combination of the video camera and the computer, connected to it for the analysis of the electric image signal, has become available. Since then, several research groups have directed their work to processing of pictures taken of the flotation froth, either in order to determine structures of froths from black/white pictures (e.g. Moolman D. W. & al. in Int. J. Miner. Process. 43(1995), 193-208) or colors of froths from multi-, i.e. usually three-color pictures (e.g. Oestreich J. M. & al. in Minerals Engineering 8(1995), 31-39). Apparatuses with their software used for these aims have since then been subjected to commercialization. It is typical to said studies and apparatuses to observe a rectangular, rather large part of the industrial cell's froth surface, whose horizontal area is typically considerably larger than one square meter, and to process the sampled surface of said type as a representative sample of the cell's froth surface.
The conventional semiconductor matrix video camera device has been used in the stated studies. The U.S. Pat. No 4,831,641 states, for its part, the analysis of flowing suspension in the mineral refining industry and, more particularly, the identification of solid particles in a flowing process fluid, without distinguishing the semiconductor matrix and semiconductor line array cameras from each other. It does not mention the flotation froth, and with suspensions in the stated industry one usually means two-phase solid/liquid suspensions and not the three-phase flotation froth. The illumination of the object is not presented at all in the stated patent.
An individual bubble can, if the camera and light source are located above the cell, be distinguished by means of light, which is reflected strongly back by its top area. This small, bright spot is in such a case surrounded by a darker zone. Depending on the illumination, the darkest regions may lie at the border of two bubbles, but the bottom of the valley separating the bubbles appears often also bright, because of the light it reflects, or is manifested by a stepwise change of the degree of darkness. Determination of the structural parameters of the froth, such as the mean bubble size and the form, density and size distribution of the bubbles can, further on, be based on the borderlines. The speed of the froth's movement is, for its part, determined by comparing successive pictures with each other. It is also customary to determine the brightness distribution of the imaged area and to present it in the form of a histogram. Features of the structure can also be determined by means of other statistical methods, on the basis of the frequency of appearance of image elements of different degrees of darkness.—The deterministically and statistically determinable features stated above are examples of quantities which have been determined by image analysis and presented in the literature, and which are generally characterized by a considerably large scatter.
By means of a color video or color television camera one obtains, of the imaged field of the same type, a red, green and blue (RGB) signal, which signal set or the composite signal of standard form corresponding to it can be processed as such or transformed to other code form before processing. Determination of the color or spectrum of the froth suffers from large differences of intensity of the light reflected specularly or diffusely by the froth. Therefore e.g. too high signal elements have to be removed before processing. The color observed depends on mineral composition of the froth, but the determination of this dependence meets difficulties in practice which, in addition to the said differences of intensity, is due to the rather small differences of color of the colored metal minerals and to other, generally black/gray/white minerals present and to variation of their concentrations. Determination of both the structure and color is affected by the inhomogeneity of the quantities observable in the fields of view of the said camera instruments. This has not been taken into account in the studies reported earlier and has at least not influenced their methodologies or hardware technologies; it shall be reverted to lower down.
For the stated determinations described in the literature, one has used previously known computational algorithms or mathematical methods, which have been programmed to the form required by numerical computation in accordance with the aim of use described, or are obtainable from software libraries (See e.g. Niemi A. J. & al. in Int. J. Miner. Process. 51(1997), 51-65 and several of its reference publications). Results of the determinations can be exploited in flotation control, but because their dependence on the input quantities of flotation is generally not accurately nor unambiguously known, the statements on control and regulation have remained on the stage of draft in the literature.
PARTICULAR BACKGROUND OF THE INVENTION
In an ideally operating flotation cell, the entering air is distributed symmetrically around its axis in the horizontal plane, an the bubbles are distributed homogeneously, still as they reach the lower interface of the froth layer. The froth leaves the cell, which typically has the form of a rectangular parallelepiped, over one of its edges, or sometimes over its two opposit
Rosenberger Richard A.
Thorpe North & Western
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