Lime Ash Research Articles

Leaching characteristics of residual lateritic soils stabilised with fly ash and lime for geotechnical applications

The effective use of residual lateritic soils as fill material for various construction activities is often limited by the difficulty in handling them. Attempt to improve their workability with fly ash and lime has shown promising results, although accompanied by risk of release of heavy metal leachates to the groundwater. In the present work, the leaching properties from residual lateritic soils from a part of Northeast India stabilised with fly ash and lime (CaO) was investigated with the help of single batch leaching test and column leaching test for different soil–fly ash–lime mixes. Test results show that the high pH induced by lime treatment of the mixes helps in keeping most of the metals within the stabilised soil matrix. Although the heavy metal concentrations in the leachates were generally within permissible limits, the release response for different metals was different suggesting implications for permeate solutions having metal pre-concentrations, such as those emanating from hazardous landfill sites. The observed characteristics provide insights towards the potential and realistic estimates of leaching of metals and its variation due to change in fly ash and lime content in the stabilised mix. Many of these constituents found in the stabilised soil had a first-flush phenomenon. But, as they occur only for short duration (about 5 pore volumes over 5 days) and at low concentration, dilution effect may eliminate them. The effect of continuous permeation on the flow parameters and the leaching pattern of the mixes have also been highlighted.

Characterisation of sugar cane straw waste as pozzolanic material for construction: Calcining temperature and kinetic parameters

This paper reports on the influence of calcining temperature (800 and 1000 °C) on the pozzolanic activation of sugar cane straw (SCS). The reaction kinetics of SCS ash–lime mixtures were inferred from physicochemical characteristics (X-ray diffraction patterns and thermogravimetry analysis. The fitting of a kinetic–diffusive model to the experimental data (fixed lime versus time) allowed the computing of the kinetic parameters (reaction rate constant) of the pozzolanic reaction. Results obtained confirm that the sugar cane straw ash (SCSA) calcined at 800 and 1000 °C have properties indicative of very high pozzolanic activity. No influence of calcining temperature on the pozzolanic activity was observed. Also, no crystalline compounds during the pozzolanic reaction were identified up to 90 days of reaction. Environmental durability and strength of the consequential mortars remain to be assessed.

Chemical processing of a low grade molybdenite concentrate to recover molybdenum

The conventional oxidative roasting process, as applied to high grade molybdenite ores (containing ≥54% molybdenum), cannot be applied to low grade sulphide ores/concentrates for a variety of reasons. That is why these ores/concentrates require alternative processing schemes to extract molybdenum metal in a quantitative manner. The present investigation deals with two such processes, namely, soda ash roasting and lime enhanced carbothermic reduction that were successfully applied to extract molybdenum from an indigenous (and low grade) molybdenite concentrate (MoS2).These processes yielded molybdenum in the form of molybdenum trioxide (MoO3) and molybdenum metal respectively. MoO3 and molybdenum metal, so prepared, were further refined by carbon adsorption desorption and molten salt electrorefining techniques respectively. The final purity of MoO3 and molybdenum metal were 99·9% and 99·8% respectively. These processes offered effective measures to contain environmental pollution and bypass tedious off gas treatment procedures, which, otherwise, are two major problem areas in the traditional processing of high grade MoS2 ores/concentrates.

Study on the weathering resistance of fly ash–lime compacts

The relationship between the inner quality factors (such as the amount of effective calcium oxide and the pore structure) of steam-cured fly ash–lime compacts (clinker-free) and the environment factors (such as drying shrinkage, freeze–thaw and carbonation, et cetera) have been studied here comprehensively by the simulation weathering examination. Meanwhile, the influences of additives of alkali paste and gypsum on the mechanical properties and pore structure of the compacts have been investigated and discussed, and the effects of interface texture on the mechanical properties have been discussed also. The results suggest that the weathering resistance of the system studied can be improved effectively by means of controlling the fraction of effective calcium oxide (EF cao) and additives, in turn, to improve the interface interlinking. The optimum fraction of EF cao is ∼15.3%, alkali paste is about 3.0% and gypsum is 1.7∼2.6% (account by SO 3%) if the as-received low calcium-bearing fly ash with low carbon content (<6.0%) has been selected.

A perspective study on fly ash–lime–gypsum bricks and hollow blocks for low cost housing development

Housing is a great problem in today's world. The most basic building material for construction of houses is the usual burnt clay brick. A significant quantity of fuel is utilized in making these bricks. Also, continuous removal of topsoil, in producing conventional bricks, creates environmental problems. A feasibility study was undertaken on the production of fly ash–lime–gypsum (FaL-G) bricks and hollow blocks to solve the problems of housing shortage and at the same time to build houses economically by utilizing industrial wastes. The compressive strength, water absorption, density and durability of these bricks and hollow blocks are investigated. It is observed that these bricks and hollow blocks have sufficient strength for their use in low cost housing development. Tests were also conducted to study the influence of type of curing on the increase in strength and hardening of the bricks and blocks with time. It was observed that the hot water curing leads to a greater degree of hardening and higher strength, earlier compared to ordinary water curing.

Fly ash–lime–phosphogypsum hollow blocks for walls and partitions

Fly ash–lime–phosphogypsum (FaL-G) hollow blocks are one of the best substitutes for conventional burnt clay hollow bricks or concrete hollow blocks in construction industry. FaL-G hollow blocks are light in weight and being hollow, impart thermal insulation to the buildings. In this paper, a study based on the results of an experimental investigation on FaL-G hollow blocks is presented. The compressive strength, water absorption and weight of FaL-G hollow blocks were determined. The durability of these blocks in terms of loss in compressive strength in sulfate environments is also presented in this paper. It is observed that FaL-G hollow blocks have sufficient strength for their use in general building construction.

Study of the effect of fly ash on desulfurization by lime

Fly ash was used as an additive, and the effect of it on desulfurization by lime at 400–800°C was studied experimentally. The conversion rate of fly ash–lime to calcium sulfate was found to be greater than that when using lime alone. One reason is that fly ash can act as a support medium for lime, thereby increasing its dispersion and extending its effective reaction surface area. Fly ash with a high iron or its oxides is likely to have some ability to absorb particles of lime on its surface.

Pozzolanic behaviour of bagasse ash

The CBRI investigations indicate that bagasse ash has to be considered as a pozzolanic material like fly ash or any other conventional pozzolana. High surface area is required to expose the grains which are coated with iron oxide and carbonaceous impurities. The authors consider that the material may be used for preparing lime ash mixture to be used locally as a mortar, especially in rural areas where availability is high.