Stable Heap Research Articles

Recovery of nitrates from leaching solutions using seawater

The objective of this work is to investigate the use of seawater to recover potassium and nitrate from the waste tails of SQM operations. The use of seawater as an alternative to fresh water is an attractive option for the resource-rich northern Chilean mines, especially for those operating in the Salar de Atacama Desert where fresh water is scarce.In this study, the performance of four leaching agents was evaluated for recovering potassium and nitrate from discarded salts: 1) freshwater; 2) seawater; 3) seawater saturated with chloride ions; and 4) seawater saturated with chloride, sulfate and magnesium ions. The tests were performed in columns loaded with the same quantity of salt and irrigated at the same rate for a period of 152hours. These tests showed that leaching with seawater provides nearly the same potassium and nitrate leaching efficiency as when fresh water is used. However, leaching with seawater saturated with chloride, sulfate and magnesium ions yielded approximately 10% lower potassium and nitrate recoveries compared with the tests when seawater was used alone. In contrast, the use of saturated seawater is expected to yield a geomechanically more stable heap because most of the chloride-, sulfate- and magnesium-containing salts will remain unleached.

Drum agglomeration behavior of nickel laterite ore: Effect of process variables

Heap leaching is a promising, economically viable processing pathway for extracting nickel (Ni) and cobalt (Co) from complex, low grade laterite ores. Producing a stable heap with high permeability and sustainable lixiviant percolation rate is a key requirement to ensure efficient leaching operation for maximum value metal recovery. Agglomeration of fine ore particles to produce robust granules with desirable attributes (e.g., size distribution and strength and porosity) is a critically important precursor to the heap leaching process. In this study, the effect of binder type/composition and dosage, drum speed, temperature and batch time on drum agglomeration behavior of siliceous goethite (SG) Ni laterite ore was investigated. Isothermal, batch agglomeration performed with tap water and 30, 44 and 98%w/w H2SO4 solutions as binders revealed the key role of binder dosage and acidity in controlling ore particle wettability, granule nucleation and growth behavior. Increasing the binder acidity from zero (tap water) to 30, 44 and 98%w/w H2SO4 led to a higher binder dosage to initiate and maintain a moderate rate of agglomeration. This accordingly reflected decreasing growth rates with increasing binder acidity where 98%w/w H2SO4 resulted in complete suppression of granule growth. At a fixed binder acidity and dosage, both higher temperature and drum speeds led to faster agglomeration rates. The impact of binder acidity and dosage on agglomerates' wet strength appeared to be insignificant. Acid-bound, wet agglomerates' integrity/stability in solution was, however, greater at lower binder dosage and/or binder acidity. The findings foster our understanding of how various, primary process variables may be prudently controlled to produce Ni laterite agglomerates with desirable properties and behavior, as a key step to enhance heap leaching.

Heap formation in two-dimensional granular media

Using molecular dynamics (MD) simulations, we find the formation of heaps in a system of granular particles contained in a box with oscillating bottom and fixed sidewalls. The simulation includes the effect of static friction, which is found to be crucial in maintaining a stable heap. We also find another mechanism for heap formation in systems under constant vertical shear. In both systems, heaps are formed due to a net downward shear by the sidewalls. We discuss the origin of net downward shear for the vibration induced heap.

Atomic incremental garbage collection and recovery for a large stable heap

A stable heap is storage that is managed automatically using garbage collection, manipulated using atomic transactions, and accessed using a uniform storage model. These features enhance reliability and simplify programming by preventing errors due to explicit deallocation, by masking failures and concurrency using transactions, and by eliminating the distinction between accessing temporary storage and permanent storage. Stable heap management is useful for programming languages for reliable distributed computing, programming languages with persistent storage, and object-oriented database systems. Many applications that could benefit from a stable heap (e.g., computer-aided design, computer-aided software engineering, and office information systems) require large amounts of storage, timely responses for transactions, and high availability. We present garbage collection and recovery algorithms for a stable heap implementation that meet these goals and are appropriate for stock hardware. The collector is incremental: it does not attempt to collect the whole heap at once. The collector is also atomic: it is coordinated with the recovery system to prevent problems when it moves and modifies objects. The time for recovery is independent of heap size, even if a failure occurs during garbage collection.

Atomic garbage collection: managing a stable heap

Modern database systems use transactions to achieve a high degree of fault-tolerance. Many modern programming languages and systems provide garbage collected heap storage, which frees the programmer from the job of explicitly deallocating storage. In this paper we describe integrated garbage collection and recovery algorithms for managing a stable heap in which accessible objects survive both system crashes and media failures. A garbage collector typically both moves and modifies objects which can lead to problems when the heap is stable because a system crash after the start of collection but before enough of the reorganized heap reaches the disk can leave the disk in an inconsistent state. Furthermore, collection has to be coordinated with the recovery system. We present a collection algorithm and recovery system that solves these problems.