Currently, heap-leaching operations are plagued by poor permeability of the heap, which leads to uneven distribution of the leaching solution, unleached zones in the heap, and low metal recovery. This poor permeability is caused by excessive amounts of fine particles clogging the spaces between larger ore particles. By agglomerating ores, individual ore particles will be held together in coarse, porous masses with the use of a binder. In addition to benefits for heap leaching, agglomeration is a critical factor in the success of the Iron Ore Industry. This process requires the formation of strong agglomerates of coal, iron oxide, and flux without heat treatment, and at a minimal cost.
Unfortunately, there are no known agglomeration binders that will work satisfactorily in the acidic environment encountered in many heap-leaching operations, and few binders that will produce high strengths without sintering. Alkaline binders, for instance, are destroyed by acid attack, and are thus completely unsuitable for use in acidic leaching heaps. Other binders are synthetic polymer compounds, but many of these binders also perform poorly in acidic environments. In most cases their synthesis costs are so high that they are impractical. As a result, operators of acidic heap-leach facilities cannot take full advantage of the agglomeration technique.
Because of problems with effectiveness or cost, all binders that have been evaluated to date for use in acidic heap leaching have either performed poorly, or proved to be too expensive for commercial use. Furthermore, mixing problems in all types of heap leaching operations has led to significantly more binder usage than necessary. The large quantity of ore that must be handled in heap-leaching operations requires that the binder must be kept to low dosages to be economical.
Researchers will select the binders to be studied in this project based on theoretical considerations, with particular emphasis on low-cost reagents or industrial wastes/ byproducts that are expected to be particularly acid-resistant. The use of advanced compressive shear mixing technology will further reduce binder cost by ensuring that the binder is used with the greatest possible efficiency. Michigan Technological University, along with their project partners, will focus on developing a more broadly usable binder and a more efficient binder/ore mixing method that will benefit all heap-leaching operations that use agglomeration. The project will improve energy efficiency by increasing metal recovery during heap leaching, reducing the quantity of ore that must be handled and prepared to produce a given amount of metal.
Another result of the project will be the decreased land area required for leaching pads due to the increased processing efficiency, which not only reduces cost, but also simplifies design to prevent spills and groundwater contamination. Boosting the use of heap leaching will also generate lower emissions than are currently generated by conventional smelting techniques. The binders developed are expected to benefit the agglomeration of feed pellets for use in the Iron Nugget process, which will make it possible to implement this process as a high-efficiency, environmentally-sound replacement for blast furnace technology.
