Slate Waste Research Articles

Fertilizer application during primary succession changes the structure of plant and herbivore communities

Fertilization of secondary successional communities generally increases biomass but reduces diversity; its impact on primary successional communities is less well understood. Following applications of a balanced fertilizer to naturally established vegetation on slate quarry waste, effects on tree growth, ground flora species and foliar invertebrates were monitored over two years. Fertilization increased tree growth, with stem basal area increasing by 130% over two growing seasons compared with a 50% increase in unfertilized trees. Several dominant ground flora species increased in cover as a result of fertilization. In contrast, cover of bryophytes was not increased. Fertilization favoured plant species associated with drier habitats, but disadvantaged less-competitive ruderal species. Tree foliar invertebrates were less abundant on the trees on slate waste than on trees in established woodland. Fertilization made tree leaves more palatable by increasing nitrogen and reducing soluble polyphenol concentrations, and increased the abundance of sap-sucking invertebrates, without changing foliar invertebrate diversity. Overall, fertilizing this primary successional site was beneficial for biodiversity; it increased abundance of dominant plant species and foliar invertebrate herbivores, yet few taxa were adversely affected during this period. Increases in tree biomass and invertebrate abundance are likely to favour the establishment of other taxa. Where the biodiversity conservation interest is principally in closed-canopy vegetation, applying fertilizer is a cheap, comparatively non-intrusive and effective way to increase biodiversity on denuded sites. However, plant species characteristic of open and infertile habitats (particularly bryophytes) and their obligate herbivorous invertebrates are likely to decrease in abundance.

Ceramic foams manufacturing from slate wastes

The objective of the present work is the recovery of slate wastes into a raw material for the ceramic industry. Foams are obtained without any addition of foaming agent thanks to the transformation of component present on the slate during heating. A glass base material with a closed porosity, gray color and density value around to 0,3g/cm 3 has been obtained. Raw material is the slate waste as slurry, after cutting roofing slates. After drying, the slate powders were die pressed to achieve green samples, which were sintered in N 2 -5%H 2 atmosphere at different temperatures, as well as in air as reference material at 1150°C. Dilatometer behavior was studied on die pressed slate powders under both atmospheres as well as X-Ray diffraction in order to determine the crystalline phases on sintered materials. Sintered density decreases as temperature increases under non-oxidant atmosphere, which leads to decrease the mechanical properties with the temperature when the foam structure is developed (over 1075°C on N 2 -5%H 2 atmosphere).

Thermal expansion of slate wastes

Among the technological routes for recycling mining and beneficiation slate wastes, thermal expansion seems particularly attractive, yielding products adequate for use in civil construction, especially as pozzolanic material for cement manufacture. The present investigation aims at analysing the properties of slate before and after the thermal expansion, searching for the reasons of expansion and the variables that affect the characteristics and properties of the products. Results of standard test procedures recommended by the construction industry are presented and discussed.

Markets for industrial mineral products from mining waste

Abstract The composition of mining waste varies according to the nature of the mining operation and many other factors, but where the same mineral is extracted from a similar style of metalliferous or industrial mineral deposit or coal, the waste usually has similar characteristics. There are many potential sources of industrial minerals from mining waste. Waste from one mine may be a byproduct or coproduct in a mining operation elsewhere. Much technical research work on mine waste utilization, for example studies on slate waste, has included a manufacturing process. The waste is invariably an inferior material compared with an industrial mineral from a primary resource for the manufacturing process. Successful markets have not been found. Four scenarios are proposed where an industrial mineral product made from mining waste may be marketed successfully. These are a bulk product for a local market made with minimal or no processing; a low unit value product and a cost-effective alternative source of a mineral for local industry; an industrial mineral commodity traded nationally or internationally; and extraction of a high unit value rare mineral. Making an industrial mineral product from mining waste and successfully marketing it should involve minimal processing of the waste consistent with the value of the mineral product.

Model and field studies of the degradation of cross-linked polyacrylamide gels used during the revegetation of slate waste

Cross-linked polyacrylamide gels are increasingly being used in environmental restoration schemes and horticulture as a means of enhancing water supply to plants. However, the environmental impact of cross-linked polyacrylamide gel deployment in soil remains poorly understood. This study assessed the chemical, physical and biological properties of new and field-conditioned cross-linked polyacrylamide gels. Both monomeric acrylamide (11 μg l −1) and acrylic acid (285 μg l −1) were observed in new gel; however, the levels of monomers in field-conditioned gels (1–6 years old) were very low (acrylamide <1 μg l −1; acrylic acid <7 μg l −1). Generally, freeze–thaw processes and exposure to UV radiation had little effect on gel acrylic acid and acrylamide concentrations. However, elevated temperatures (35 °C) caused a significant release of up to 144 μg l −1 of acrylamide and 453 μg l −1 of acrylic acid in new gel and up to 25 μg l −1 of acrylamide and 157 μg l −1 of acrylic acid in field-conditioned gels. In contrast, gel water holding capacity was highly dependent upon environmental conditions (UV exposure and freeze/thaw cycles produced the greatest loss of water holding in new gels) and gel age. Optical microscopy revealed that after placement in the field the gels became increasingly colonised over time by fungi and bacteria. In enrichment cultures, we were unable, however, to demonstrate microbial growth when cross-linked polyacrylamide was used as the sole nitrogen source. In summary, under a range of conditions cross-linked polyacrylamide did not release acrylamide above legally permitted limits, with the exception of gel subjected to elevated temperatures. However, their capacity for holding water decreased sharply within 18 months. We therefore conclude that cross-linked polyacrylamide placed in soil is relatively stable with respect to the production of potentially toxic acrylamide, a species with a short half-life, which degrades to the much less toxic acrylic acid. However, the loss of water holding capacity raises questions about its long-term effectiveness in land restoration schemes as this is the main reason it is used in this role.

Production and characterization of ceramic pieces obtained by slip casting using powder wastes

The growing world population in industrialized countries is resulting in an increasing consumption of raw materials and thus in a flood of waste. The recycling of materials and waste treatment techniques have drawn the attention from all different areas including industries, technology centers and universities. In the present work the main objective is to recover wastes from slate rock industry, using powder technology by slip casting process to produce ceramic pieces. The characterization of slate powder according to its mineral composition shows the presence of minerals like quartz, chlinoclore, albite, orthoclase and muscovite, which could be used as raw materials for ceramic products. We also have noted a close dependence on powder and additive concentration with the viscosity of suspension. The sintering study was accomplished through density and porosimetry essay, surface area evaluation among others. X-ray results coupled with thermal analysis have clearly indicated major structural transition at 500 and 900 °C. The results obtained after sinterization to 1000 °C showed that the sintering strongly influenced the structural transition occurred in slate. The results allow us to conclude that slate wastes can be used in the manufacture of ceramic pieces by slip casting. The optimized properties of pieces to different uses can be achieved by controlling the powder characteristics, the molding process and the sintering conditions.

Recovered slate waste as raw material for manufacturing sintered structural tiles

Since roofing slate exploitations generate large quantities of slag from the quarry and mud from the cutting tools, special efforts are needed to avoid associated environmental hazards, such as floods and the unsightliness of slag-heaps. Recovering this mud and slag as raw material for manufacturing sintered structural parts could be a response to the demand. This study, which includes a characterisation of the material and an evaluation of the final properties, examines the raw material and its behaviour during compaction to determine whether it is suitable for processing by powder technology. A mineralogical characterisation by chemical analysis and X-ray diffraction, together with a thermal analysis, provided the data of the sintering process. The properties of the sintered samples were checked by: density, dimensional change, volume loss, mass decrement, three-point bending strength, water absorption and permeability, and wear behaviour trying to guarantee their behaviour.

Powder Injection Moulding to Recover Slate Wastes

This paper focuses on the use of new technologies of ceramic manufacturing for the recovery of wastes resulting from cutting and grinding of slates. Slates are commonly used for roof and floor tiles and billiard tables. Several tonnes/day of waste can be produced. After pressing and sintering, the physical, chemical, and mechanical product properties open new approaches for the recovery of these inorganic wastes. The particle size of slate wastes is suitable to injection moulding, for the production of large series of parts with complex shapes. In this study, a method for feedstocks preparation based on slate was optimised, and the influence of thickness of moulded parallelepiped bars on debinding cycle studied. Finally, the debinding and sintering treatments were performed to evaluate some physical and mechanical properties of the final product.

An investigation of some alternative aggregates for use in concrete

Abstract The use of some waste materials as aggregate for concrete has been investigated. Three specific materials were examined, china clay waste, slate waste and pulverized fuel ash. The project investigated methods of utilising alternative materials as aggregate either by low cost processing, novel mix design or by the use of admixtures.

Behavior of Some Pavement Foundation Materials Under Repeated Loading

A wide range of alternative materials for pavement construction were studied, and assessment techniques to enable and increase their use were developed. Five secondary materials and a conventional crushed granite were considered for use in an unbound form or lightly treated with various binders (including primary and secondary binders) in a total of 11 road pavement subbase materials. The secondary materials studied were minestone, china clay sand, slate waste, fly ash, and furnace bottom ash. The laboratory program set up for this research essentially was based on repeated-load triaxial tests, and the techniques used for specimen preparation, conditioning, and testing for resilient behavior are described. In particular, the modifications of the procedures recommended by the European Committee for Standardization necessary for testing secondary materials are identified and described. The analysis of the resilient behavior of the materials studied led to the identification of two groups with identical characteristics: unbound type of behavior (which included lightly treated mixtures), and treated type of behavior. A definition of boundaries for those groups was attempted. The mechanical properties of these materials necessary for use in analytical methods of pavement design are also presented, and the implications of treatment in terms of triaxial strength and resilient modulus are discussed.

Assessment of secondary materials for pavement construction: Technical and environmental aspects

Current research at the University of Nottingham to enable the use of secondary materials in road construction covers technical aspects, mechanical properties of waste materials and the environmental implications of their use. Materials studied are minestone, china clay sand, slate waste, pulverised fuel ash and furnace bottom ash. The laboratory programme set up for this research and the methodologies suggested for the study of the properties of these materials are presented. The test methods currently used to select pavement aggregates are presented along with current methods for the assessment of the environmental impact of secondary aggregates. The potential of the secondary aggregates is assessed within the current technical and environmental procedures previously presented. Two new methodologies are presented, one for the mechanical examination of secondary aggregates and one for the environmental assessment. The mechanical assessment encompasses conventional characterisation and classification tests on both unbound and lightly treated pavement materials, and fundamental tests such as repeated load triaxial tests (RLTT) and repeated load indirect tensile tests (RLITT). Some sample results are presented, suggesting the feasibility and adequacy of this methodology for material discrimination, and evaluation of mechanical properties for design purposes. The environmental assessment indicates how the leaching concentration of contaminants from intensive testing can be used as the first step in assessing the environmental acceptability of a secondary material, and the means of determining a more realistic measure of in situ performance is discussed. The advantages and advancements of the presented methodologies over the basic and inappropriate techniques currently used to assess the suitability of secondary aggregates for use as pavement construction materials are discussed.

Slate waste tips and workings in Britain : ANON (DOE), (HMSO, for Deparment of the Environment), ISBN (paperback) 0 11 752971 0, price £35.00, 1995, 144 pp

Slate waste tips and workings in Britain : ANON (DOE), (HMSO, for Deparment of the Environment), ISBN (paperback) 0 11 752971 0, price £35.00, 1995, 144 pp

Reclamation of wastes contaminated by copper, lead, and zinc

Waste materials containing toxic levels of copper, lead, and zinc, such as mine and smelter wastes, present difficult conditions for the establishment of vegetation. This article reviews the many attempts which have been made to reclaim these wastes. Inert wastes from mining and quarrying operations, such as slate quarry waste and certain colliery shales, seem to be good materials for reclaiming wastes contaminated by copper, lead, and zinc. Organic wastes, such as sewage sludge and domestic refuse, may provide only a temporary visual improvement and stabilization of the toxic materials. Nontolerant plant materials may often be planted directly on modern waste materials, which are less toxic than they were in the past. However, tolerant plant materials are needed for revegetating waste materials produced by early and more primitive extraction methods.

Autoclaved aerated concrete from slate waste Part 2: Some property/porosity relationships

A previous paper has provided some property/density relationships for a series of experimental slate-based autoclaved aerated concretes which cover a wide range of densities. The present paper goes on to discuss the corresponding property/porosity relationships for the same series. Porosity is characterised by the solid/pore volume ratio, V s/V p, which stems from a very simple physical model of the materials. Regression analysis indicates that compressive strength, flexural modulus and strength, as well as fracture characteristics, can be regarded as linear functions of V s/V p within a reasonable degree of approximation.

Autoclaved aerated concrete from slate waste Part 1: Some property/density relationships

Large quantities of slate waste exist throughout the world. Laboratory-scale investigations have suggested the possibility of making good use of this waste, in powdered form, as a raw material in the manufactured of autoclaved aerated concrete. This paper provides property/density relationships for a series of slate-based autoclaved aerated concretes which cover a wide range of densities. Compressive strength, flexural strength and modulus, and fracture characteristics have been investigated; the latter indicate that fracture surface energy, determined by the work of fracture method, at present offers the most satisfactory approach to the evaluation of toughness of these materials. The results show sufficient promise generally to indicate that these investigations should be extended further.

The supply of wild ruminants with major and trace elements. 2. The manganese content of winter grazing and the manganese status of red deer, fallow deer, roes and mouflons

The winter grazing of wild ruminants on mantles of slate waste in the Harz mountains and in Gera county were richest in Mn whereas those on mantles of granite waste in the Erzgebirge were poorest. The flora of the shell-limestone, keuper and loess areas contains much less Mn than that of those acid habitats. The Mn-requirement of the wild ruminants grazing in the forests is met however, since bilberry plants (2,080 mg/kg), spruce twigs (984 mg/kg), spruce bark (827 mg/kg), oak twigs (791 mg/kg) and heather (754 mg/kg dry matter) in addition to many other plant species store extremely high amounts of Mn. Solely sallow twigs were poor in Mn (28 mg/kg). Based on 601 samples examined, the Mn supply of wild ruminants is extensively described. The rumen content reflected the plentiful Mn-supply of the wild ruminants living in forests (greater than 400 mg/kg) and the far worse one of field roes, particularly in Mn-deficiency areas for domesticated ruminants (mantle of shell-limestone waste 37 mg Mn/kg dry matter of rumen content). The indicator organs of the Mn-status (liver, covering hair, kidneys) verify the statements made concerning red deer, fallow deer and mouflons, of which a total of 170 head from 14 biotopes were examined. An Mn-deficit of field roes in Mn-deficiency habitats in winter cannot completely be excluded. Mouflons have not yet been able to adapt themselves to the excessive Mn-supply of the acid forest habitats in Central Europe. They stored significantly higher amounts of Mn in liver, covering hair, kidneys, cerebrum and ribs than the other wild ruminants and sheep and cattle. The normal Mn-content of the liver and the cerebrum of red deer, fallow deer and roes corresponds to that of sheep and cattle. Roes and fallow deer have winter covering hair poor in Mn (less than 4.0 mg/kg) in comparison to sheep and cattle.

Ecology and the problems of rehabilitating wastes from mineral extraction

Ecology and the problems of rehabilitating wastes from mineral extraction