Heap Construction Research Articles

Three-dimensional characterisation of pore networks and fluid flow in segregated heaps in the presence of crushed ore and agglomerates

Due to the differences in ore feeds and stacking procedures, segregated pore networks are commonly observed in industrial heap leaching operations, which strongly affect the pore-scale fluid flow and the resulting metal leaching efficiency. Three segregated models, namely, the agglomeration model or AM with intra-particle pores, the crushed ore model or COM with inter-particle pores and the mixed segregated model or MSM with both intra- and inter-particle pores, are defined in this work. The segregated pore network in the MSM consists of agglomerates and crushed particles. The models were obtained by performing micro-computed tomography scanning experiments in packed beds followed by image processing algorithms. Several fluid flow-related parameters were quantified to understand the effects of segregated pore networks on fluid flow in heap leaching. The isolated and connected pores co-exist in porous ore heaps, and the latter determines heap hydrodynamics. The number of connected pores in the AM is higher than in the COM. However, the connected pores with too small pore throats are very slow in fluid transfer by capillarity, resulting in stagnant regions in ore beds. A smaller tortuosity value was also observed in the COM, resulting in fast-flowing preferential fluid flow paths. These are unfavourable to yield uniform fluid flow distributions in industrial heaps. The results of this work suggest the prerequisites for improving fluid flow distribution in heaps, including well-organised heap construction procedures, controlling the particle size distribution and large-scale studies coupled with non-invasive imaging and flow simulations.

Responses of bacterial community to potential heap construction methods of fine-grained copper tailings in column bioleaching system

The column bioleaching of copper flotation tailings was comparatively investigated using layered heap construction method (LM), agglomerate heap construction method (AM), and pellets-sintering heap construction method (PM). The bacterial communities of free, attached, weakly-attached, and strongly-attached microbes in the later bioleaching stage were investigated. In AM group, the addition of lump sulphide ore resulted in the low leachate pH, high ferric iron concentration, and rapid microbial adsorption, which obtained the maximum copper extraction (60.1%) compared with LM (54.6%) and PM (43.9%) groups. The relative abundance of dominant genera and microbial communities of different microbiota underwent changes in three heap construction methods. The alpha-diversity indexes of attached, weakly-attached, and strongly-attached microbes were different, while no significant change was observed in free bacteria. The variation of whole bacterial community was significantly associated with solution pH, total iron, and ferric iron concentrations. Pearson correlation analysis and partial least square path model both indicated that attached bacteria made larger contribution to the copper extraction of tailings.

The effects of packing shape and structure on liquid distribution of heap leaching systems: Addition of PCBs as non-ore particles

Heap leaching is a hydrometallurgical processing technique where the effective mass transfer between the multiple phases dictates the process efficiency. It is employed to process low grade mineral deposits, which cannot be treated economically by conventional mineral processing techniques, such as flotation followed by smelting. While the noteworthy merits of heap leaching are low capital and operational costs, a significant shortcoming is the low recovery efficiencies. Heap hydrodynamics is a vital contributor to the overall recovery as it facilitates the transport of both the chemical reagents and the dissolved metal species. Although a uniform liquid distribution is a requisite for an improved metal recovery, often an anomalous liquid distribution (liquid channelling) is observed in industrial heaps. This study explores the effect of the heap packing structure on heap hydrodynamics by introducing non-ore particles as a packed bed modification strategy, which is analogous to novel heap construction methods. It was studied by introducing planar printed circuit board (PCB) pieces (25*25 mm2 and 50*50 mm2) and those were used to form the layered and mixed packed beds. Out-flow liquid distribution, ultraviolet (UV) fluorescence based flow paths visualisation, liquid holdup measurements, and liquid mal-distribution factors were determined and the results were compared again with the same given by the two control packed beds, namely, the ore bed and the PCB bed. The out-flow liquid distributions and liquid holdup profiles were combined to asses heap hydrodynamics and mass transport mechanisms. The layered beds and the mixed bed with larger PCB pieces contributed to a widely distributed out-flow profile by creating more liquid flow paths and thus the channelling effect was alleviated. The result of this work could be used to develop novel heap construction techniques with further studies on introducing non-ore particles into ore systems.

Influence of particle size on copper recovery from sulfide ore by the moderately thermophilic microorganisms

The bioleaching of copper ore by the defined moderately thermophilic consortium containing Leptospirillum ferriphilum and Acidithiobacillus caldus was carried out in the bench-scale column. Bioleaching experiments showed that the leaching rate was 25% higher than that of a conventional leaching and the acid consumption was reduced by 33% at the optimal leaching condition. Meanwhile, the effect of different particle sizes on the rate of the copper leaching was also investigated, and it was shown that the particle size affects the bioleaching rate significantly in the range of 5–25 mm, in which approximately 89.27% of copper was extracted at 5–10 mm, while only 57.08% at 15–25 mm. The results obtained by X-ray diffraction (XRD) analysis of the mineral samples before and after microbial and chemical leaching revealed that the decrease in particle size of the minerals resulted in an enhancement of complex microbial interactions. Especially for the particle size of 5–10 mm, a significant amount of elemental sulfur and jarosite formed on the surface of the mineral, while it was further confirmed that critical microbe-mineral interactions have taken place on the mineral surface. The results indicated that mineral particle size is an integral factor to improve the copper recovery from ore in heap leaching operation. This will provide a reference to the heap construction for the bioleaching.

Heap Construction—50 Years Later

Heap Construction—50 Years Later

The effect of potential heap construction methods on column bioleaching of copper flotation tailings containing high levels of fines by mixed cultures

It is known that excess fines may reduce heap permeability and block channelings of leachate flow in heap bioleaching operation, and further cause low metal recovery. The purpose of this investigation was to compare the effects of three potential heap construction methods including layered heap construction method (Method A), agglomerate heap construction method (Method B) and pelletized sintering heap construction method (Method C) of copper flotation tailings on column bioleaching behaviors. In the three heap construction methods, the tailings copper extractions achieved 54.61%, 60.09% and 43.93%, respectively, in Method A, B and C on day 83. Copper extraction of Method B reached maximum. In addition, compositions and structures of microbial communities were examined using Illumina Miseq sequencing technology based on 16S rRNA amplification. Acidithiobacillus, Leptospirillum and Ferroplasma were main microorganisms in three heap construction methods. Detrended correspondence analysis showed that Method C had little effect on microbial communities. These studies revealed the influence of different heap construction methods on leaching behaviors and microbial dynamics, which will facilitate the bioleaching of fine-grained ores.

Geotechnical investigation and design of leaching heap No. 2, Meydook copper mine, Iran

The main objective of this paper was to investigate the behavior of waste rock material as a foundation for the construction of leaching heaps. In mountainous open pit operations, selection of an appropriate location for dumping waste rock material or building leaching heaps is a major challenge. Meydook copper mine is one of the largest copper operations in Iran. The mine has operated about 2 decades. The current waste rock dump is located 4km from the operation site but a new proposed dump only 1km away will be built in a valley to the North of the pit. Construction of leaching heap No. 2 has been on the mine technical department agenda. The main objective of the project is to evaluate the potential for construction of heap No. 2 on a waste dump. Considering the project condition, a 3D analysis of heap major structures including; valley rock foundation, waste dump, and low grade ore was carried out. Five sets of analyses were conducted and the displacement and stress fields were computed. In all analyses conducted, the subsidence profile was determined for the valley base rock and heap foundation (waste dump). The analyses showed that the maximum settlement at the heap base would be only 4–5cm so the waste dump provides a safe and reliable base for the heap construction. A sensitivity analysis of heap mechanical parameters was also conducted. The results showed that if the friction angle of heap material was reduced below 25°, the heap walls became unstable and the heap geometry would need to be redesigned.

Long-term persistence of seeded grass species: an unwanted side effect of ecological restoration

Spoil heaps are the visible footprint of hydropower production, particularly in vulnerable alpine environments. Speeding up vegetation development by seeding commercial grass species has been a common restoration practice for the last 50years, but we lack information on whether seeded species decline and allow native plant cover to develop. We visually estimated cover of native vascular plants and five seeded grass species (Agrostis capillaris, Festuca ovina, Festuca rubra, Schedonorus pratensis and Phleum pratense) on eight spoil heaps at different elevations (boreal-alpine zone) in western Norway. Spoil heap vegetation was censused twice (9-20 and 24-36years after spoil heap construction); the undisturbed surrounding vegetation was also censused on the second occasion. Total cover on the spoil heaps showed some increase, but remained far below that in surrounding areas. Cover of seeded grass species in the surroundings was low (but not negligible), indicating suboptimal establishment ability. Seeded species usually covered less than 20% of the spoil heaps, and only F. rubra, F. ovina and A. capillaris contributed substantially. Proportional cover indicated better initial establishment by seeded species, but their cover decreased between the censuses on all but the highest located spoil heap. The persistence of seeded grass species is problematic, and despite the decrease in proportional cover, they are likely to persist for decades on spoil heaps, posing a risk of invasion of surrounding areas. We therefore recommend replacing the practice of seeding with more appropriate restoration measures.

On-line construction of position heaps

We propose a simple linear-time on-line algorithm for constructing a position heap for a string (Ehrenfeucht et al., 2011 [8]). Our definition of position heap differs slightly from the one proposed in Ehrenfeucht et al. (2011) [8] in that it considers the suffixes ordered in the descending order of length. Our construction is based on classic suffix pointers and resembles Ukkonen@?s algorithm for suffix trees (Ukkonen, 1995 [17]). Using suffix pointers, the position heap can be extended into the augmented position heap that allows for a linear-time string matching algorithm (Ehrenfeucht et al., 2011 [8]).

Modeling the effect of stratification on cemented layer formation in sulfide-bearing mine tailings

Abstract Reactive transport simulations have been applied to investigate possible effects of stratification on the potential of sulfide-bearing mine tailings to form protective cemented layers. The simulations are based on characteristic strata found at a German tailings site, including sulfide-enriched heavy mineral layers, mica-enriched silt layers, and homogeneously mixed layers. The simulated secondary phases (jarosite, gypsum, amorphous ferric arsenate, amorphous Fe hydroxide, alunite, amorphous silica, and kaolinite) are similar to those observed in the field. Using scanning electron microscope analyses of cemented layers, it has been observed that the pore area becomes disconnected if the porosity is decreased to values below 15%, which would indicate a strong decrease in permeability. Stratification was found to play a crucial role in cemented layer formation. Cemented layers are absent or insignificant in systems with a homogeneous distribution of Fe-bearing sulfides. They are extensively developed in systems with (a) an arsenopyrite-rich layer or (b) a mica-enriched layer situated immediately below an Fe-sulfide enriched layer. The modeling results have clearly demonstrated that the key processes operating in scenario (a) are very different from the key processes in scenario (b). In scenario (a), the oxidation of arsenopyrite is followed by the precipitation of amorphous ferric arsenate, which can be solely responsible for significant pore reduction. In scenario (b), the presence of a large amount of reactive aluminosilicates (e.g. biotite and Ca-bearing plagioclase) immediately below the Fe-sulfide rich layer appears to be crucial. Key processes are extensive formation of Acid Rock Drainage (ARD) followed by enhanced (pH-driven) weathering of aluminosilicates, resulting in the accumulation of secondary phases directly below the Fe-sulfide rich layer. In both scenarios, a cemented layer is formed that effectively retards the further downward movement of the oxidation front. The presented details on the role of stratification in the formation of cemented layers could be considered in the construction of mining heaps as a possible measure to stimulate natural attenuation.

Restoration of alpine spoil heaps: Successional rates predict vegetation recovery in 50 years

Human disturbances in the alpine region can have long-lasting ecosystem effects because biological recovery in harsh environments proceeds slowly. As a by-product of the exploitation of hydroelectricity, surplus masses from tunnel excavations are deposited as spoil heaps in the alpine landscape. The typical management goal for such spoil heaps is that their species composition converges towards that of their undisturbed surroundings. At present we lack knowledge of the rate as well as the direction of these successions. We examined the species composition of five alpine spoil heaps in western Norway at two points in time, after 6–16, and 24–34 years of succession, with regard to vegetation cover, species richness, species composition and soil conditions. We also compared the vegetation of spoil heaps with that of their surroundings. After ca. 30 years, bryophyte and lichen cover and species richness were similar to those of their surroundings, while cover of vascular plants and species richness recovered more slowly. The vegetation development of spoil heaps appears safe-site limited rather than dispersal limited. Topsoil development was slow, but some accumulation of organic matter was observed. The species composition followed a successional trajectory in direction of the vegetation of the surroundings. Estimated linear successional rates indicate that 35–48 years are needed from construction of spoil heaps till a species composition more or less similar to their surroundings has been reached. However, these estimates are likely to be over-optimistic because successional rates tend to decrease with time. Based on our results we propose three changes to the current spoil-heap construction practice that will improve their restoration: (1) to increase surface unevenness, by which the number of safe sites will increase and germination and establishment success will be enhanced; (2) to increase substrate variability, by adding more of fine-grained materials more species will establish in shorter time; and (3) to use seed from local sources or to let the spoil heaps regenerate naturally.

Characterization, classification and land use management of flood plain soils of central Cross River State, Nigeria.

The floodplain soils of Central Cross River State are extensively cultivated for food crop production and contributes nearly 60% of the agricultural wealth of the inhabitants. Knowledge of their characteristics, classification and management will enhance their productive potential and facilitate technological transfer. Profile pits were escavated in levee and backswamp locations in two communities with extensive floodplains and studied. Based on morphological and other analytical characteristics, the soils were classified according to USDA soil Taxonomy and correlated to FAO/UNESCO soil map of the world legend. Backswamp soils were classified as Vertic Tropaquepts while levee soils were classified as Typic Tropustuepts at sub-group level of the USDA soil Taxonomy. The FAO/UNESCO equivalent of these soils is Luvisol. The major limitations of these soils are high acidity (low pH), low available phosphorus and poor drainage. Backswamp soils were superior in most fertility indices assessed than levee soils. Soil pH in these soils had a high positive correlation with CEC, available phosphorous and base saturation with “r” values of 0.79, 0.76, and 0.75 at p0.01 significant level. The floodplain soils can be efficiently managed through the use of water control mechanisms, construction of efficient low cost drainage systems, construction of giant heaps and application of phosphatic fertilizers/NPK high in phosphorus. The backswamps can be dammed for fish farming.

An Efficient Algorithm for Partial Order Production

We consider the problem of partial order production: arrange the elements of an unknown totally ordered set T into a target partially ordered set S by comparing a minimum number of pairs in T. Special cases include sorting by comparisons, selection, multiple selection, and heap construction. We give an algorithm performing $ITLB+o(ITLB)+O(n)$ comparisons in the worst case. Here, n denotes the size of the ground sets, and $ITLB$ denotes a natural information-theoretic lower bound on the number of comparisons needed to produce the target partial order. Our approach is to replace the target partial order by a weak order (that is, a partial order with a layered structure) extending it, without increasing the information-theoretic lower bound too much. We then solve the problem by applying an efficient multiple selection algorithm. The overall complexity of our algorithm is polynomial. This answers a question of Yao [SIAM J. Comput., 18 (1989), pp. 679–689]. We base our analysis on the entropy of the target partial order, a quantity that can be efficiently computed and provides a good estimate of the information-theoretic lower bound.

The bounds of min-max pair heap construction

In this paper, lower and upper bounds for min-max pair heap construction has been presented. It has been shown that the construction of a min-max pair heap with n elements requires at least 2.07 n element comparisons. A new algorithm for creating min-max pair heap has been devised that lowers the upper bound to 2.43 n.

Available stabilizing heaps

This paper describes a heap construction that supports insert and delete operations in arbitrary (possibly illegitimate) states. After any sequence of at most O(m) heap operations, the heap state is guaranteed to be legitimate, where m is the initial number of items in the heap. The response from each operation is consistent with its effect on the data structure, even for illegitimate states. The time complexity of each operation is O( lgK) where K is the capacity of the data structure; when the heap's state is legitimate the time complexity is O( lgn) for n equal to the number items in the heap.

Comparator networks for binary heap construction

Comparator networks for constructing binary heaps of size n are presented which have size O(n log log n) and depth O( logn) . A lower bound of n log log n− O(n) for the size of any heap construction network is also proven, implying that the networks presented are within a constant factor of optimal. We give a tight relation between the leading constants in the size of selection networks and in the size of heap construction networks.

Potential-Function_Based Analysis of an Off-Line Heap Construction Algorithm

Potential-Function_Based Analysis of an Off-Line Heap Construction Algorithm

On-line matching routing on trees

In this paper we examine on-line heap construction and on-line permutation routing on trees under the matching model. Let T be an n-node tree of maximum degree d. By providing on-line algorithms we prove that: 1. (1) For a rooted tree of height h, on-line heap construction can be completed within (2 d − 1) h routing steps. 2. (2) For an arbitrary tree, on-line permutation routing can be completed within 4 dn routing steps. 3. (3) For a complete d-ary tree, on-line permutation routing can be completed within 2( d − 1) n + 2 d log 2 n routing steps.

Optimal parallel construction of heaps

It is shown that Θ( n/ p + log log n) time is sufficient for constructing an implicit heap with p processors in the parallel comparison tree model. This is optimal in terms of both time and processor-time product, given the parallel lower bound for selection and the sequential lower bound for heap construction. This result resolves an open problem on the existence of time- and cost-optimal parallel heap construction algorithms.

An optimal parallel algorithm to construct a deap

Recently, Carlsson [3] proposed a variation of the heap data structure as an efficient implementation of a double-ended priority queue. This new data structure is referred to as the deap. We show that constructing a deap with special properties can be done very easily, both sequentially and in parallel, by reducing the problem to selection and heap construction. Our parallel algorithm can be implemented to run in O(log n log ∗ n) time using an optimal number of processors in the EREW-PRAM model or in O(log n) time using an optimal number of processors in the CRCW model.