Siltation of Ore Particles in Leaching Tanks: Causative Factors and Mitigation Measures

Siltation involves the accumulation of sediment over a considerable period of time and this may occur in closed systems like leaching tanks. Most mining companies in Ghana experience siltation problems during leaching of gold ore. This paper examines the potential causes and possible mitigation measures of siltation. Particle size analysis, slurry settling rate tests and agitation efficiency analysis were used in identifying causative factors of siltation whiles deflocculation test and grind analysis were conducted to ascertain mitigation measures.  Results from the study indicated that, high settling velocity of particles, inefficient milling and classification, poor slurry agitation and particle flocculation were the major causative factors leading to siltation. Size analysis results revealed P67 of 106 µm instead of P80 of 106 µm, a situation which affects particle suspension by agitators leading to siltation. This study therefore suggests that increase in milling residence time and particle deflocculation are potential remediation measures for curbing siltation. Extended grinding of ball mill feed resulted in 94% passing 106 µm while settling velocity was reduced by 71% after deflocculant addition at 1000 ppm. Keywords: Siltation, Deflloculation, Settling Velocity, Grindin

The potential of RIVPACS for predicting the effects of environmental change

RIVPACS has been used successfully for biological assessment of river water quality but its potential in forecasting the effects of environmental change has not been investigated. This study has shown that it is possible to simulate faunal changes in response to environmental disturbance, provided that the disturbance directly involves the environmental variables used in RIVPACS predictions. These variables relate to channel shape, discharge and substratum. Many impacts, particularly those associated with pollution, will not affect these variables and therefore RIVPACS cannot simulate the effects of pollution. RIVPACS was sensitive only to major changes in substratum. It was concluded that, because of the static nature of RIVPACS, it cannot respond to the dynamic effects and processes associated with environmental disturbance. Thus RIVPACS, while showing direction of change and indicating sensitive taxa, cannot be used to predict or forecast the effects of environmental impacts

Degradation of water resources in rural Burkina Faso: drivers, local perceptions and solutions.

Burkina Faso reformed its water management institutions and adopted integrated water resources management (IWRM) for more than two decades, yet the country still suffers from weak institutions and ineffective implementation of water management reforms. The key institutional question is: “How can IWRM reforms be adapted to increase effectiveness and sustainability of water management, and improve livelihoods of rural populations through increased participation of local stakeholders?” A key practical issue related to this bigger institutional question is to understand the barriers to adoption of good land and water management measures by riparian farmers and other land/water users, and the mechanisms to induce behavioral change among these users. Knowledge gaps exist in understanding the local perceptions and preferences of alternative management measures, and the incentive mechanisms to induce behavioral change. The aim of this study, which was part of a 3-year project entitled ‘Participatory planning for more inclusive and sustainable water management in rural Burkina Faso’, was to understand the perceptions, preferences and willingness of farmers and other land/water users to adopt environmentally friendly land and water management measures. The study also examined potential mechanisms that could induce riparian economic actors to adopt such measures

The Effects of Siltation on Embryonic Mortality of Trout

(print) 28 leaves : ill. ; 28 cm.In this research project, we tested the hypothesis that siltation in streams eliminates natural reproduction by increasing mortality during embryonic development. We knew that several environmental factors (temperature, dissolved oxygen, and flow rates) affected embryonic development. These factors all change with siltation in streams, but the interaction of these factors with silt needed more experimentation. If we could determine the extent to which silt alone affected embryo mortality, we could design procedures to improve trout reproduction in silted streams. In the first 18 months of our project, we tried to define the critical period of susceptibility of trout embryos to siltation. Our findings were that siltation alone did not influence embryonic development. During the remaining six months of the project we explored the effects of siltation on spawning behavior and initiated a new project to determine the feasibility of selecting trout strains, which would be more tolerant to the marginal conditions in Northeastern Ohi

Leaf Processing in a Slough of an Ozark Stream

Processing of sugar maple (Acer saccharum), black oak (Quercus velutina), and American sycamore (Platanus occidentalis) was investigated in a slough of the Illinois River, Benton County, Arkansas, using 5-gram packs in wire baskets. Oak and sycamore showed similar degradation rates, while maple was processed much faster. All processing rates were strongly retarded during a period of siltation. Chironomid larvae were the dominant organisms associated with the packs and their numbers were depressed by the silt influx. Shredders were notably few in number as compared with studies from the northwestern United States

Siltation Related to Beaver Dam Decomposition in the Little Kankakee River

The Little Kankakee River (LKR) in LaPorte County, Indiana is an uncommon example of a good, cold-water fishery in northwest Indiana. However, the river has variable sedimentation levels; deep silt often covers gravel and sand, smothering invertebrates, a key food source for higher trophic organisms. The LKR contains a naturally-decomposing, abandoned beaver dam. The purpose of this study is to monitor its impact upon upstream and downstream silt levels. This research intends to identify possible sources of variability in silt levels, benefiting restoration teams in determining effects of dam removals. Furthermore, understanding the impact and pattern of silt levels could aid the monitoring of river health. Water depth, silt depth, flow rate, and a description of the river bed are measured and recorded. Flow rate fluctuations will be charted against monthly precipitation, noting changes in flow. It is predicted that the beaver dam causes fluctuating siltation by collecting silt upstream and then releasing variable amounts during dam decomposition. Preliminary results indicate the narrow sections of the river have faster water flow and less silt. The beaver dam impedes flow, widens the river, and reduces velocity, allowing fine sediment to accumulate. It is predicted that if the beaver dam decomposes rapidly, then trapped silt above the dam will percolate rapidly through the system stopping at wide sections of the river. If the beaver dam deteriorates slowly, then silt accumulations may not be measureable and leave silt in the system much longer

Mesoscale mapping of sediment source hotspots for dam sediment management in data-sparse semi-arid catchments

Land degradation and water availability in semi-arid regions are interdependent challenges for management that are influenced by climatic and anthropogenic changes. Erosion and high sediment loads in rivers cause reservoir siltation and decrease storage capacity, which pose risk on water security for citizens, agriculture, and industry. In regions where resources for management are limited, identifying spatial-temporal variability of sediment sources is crucial to decrease siltation. Despite widespread availability of rigorous methods, approaches simplifying spatial and temporal variability of erosion are often inappropriately applied to very data sparse semi-arid regions. In this work, we review existing approaches for mapping erosional hotspots, and provide an example of spatial-temporal mapping approach in two case study regions. The barriers limiting data availability and their effects on erosion mapping methods, their validation, and resulting prioritization of leverage management areas are discussed.BMBF, 02WGR1421A-I, GROW - Verbundprojekt SaWaM: Saisonales Wasserressourcen-Management in Trockenregionen: Praxistransfer regionalisierter globaler Informationen, Teilprojekt 1DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Effects of flow regime on the young stages of salmonid fishes. Summary and conclusions based on results for 1981-1985

The main British salmonid species spawn in clean gravel in streams and rivers, many of them in the upland areas of Britain. The earliest stages of the life cycle (eggs and alevins) spend some months within the gravel of the river bed. During this period their survival rate can be strongly influenced by flow regime and by related phenomena such as movement of coarse river bed material, changes in water level and the deposition of silt. In recent years human influence upon the flow regimes of upland water courses and upon the sediment inputs to them has increased. In order to conserve and, if possible, enhance the populations of salmonid fishes a deeper understanding of the interrelationships between survival of young salmonids and flow-related phenomena is needed. The acquisition of appropriate information is the main aim of the present project, which included: Studies on silt movement and the infilling of gravel voids by fine sediments, together with initial studies on the relationship between intragravel oxygen supply rate and the survival of intragravel stages of salmonids; studies in the general field of egg washout. The latter investigated the physical background to gravel bed disruption, the examination of the physical characteristics of sites chosen for redds, dimensions of redds and burial depth of eggs relative to the size of the fish constructing the redd and a series of smaller studies on other aspects of egg washout