Nabajyoti Saikia

Characterization, beneficiation and utilization of a kaolinite clay from Assam, India

Abstract Kaolin available in Deopani, Assam of northeastern region of India was characterized by FTIR, XRD, DTA and by wet chemical analysis methods. The major impurities in the clay are quartz and siderite. Wet sieving of the clay by −53-μm sieve removes almost all the quartz and a major amount of Fe bearing impurities. The iron content of the clay may be reduced further by treating with wet high intensity magnetic separator (WHIMS) or leaching with organic acids. The effectiveness of various leachants follows the order: Oxalic>Oxalic+EDTA>Malonic>Citric acid. Almost all the nonstructural iron may be removed at room temperature by using 0.4 M oxalic acid solution. The leached clay may find use as a ceramic raw material and filler material for paper and other materials.

Kinetics of dehydroxylation of kaolin in presence of oil field effluent treatment plant sludge

Abstract Oil field effluent treatment plant (ETP) sludge contains high amounts of hydrocarbon and its disposal by land filling is a problem. Various methods to utilize the sludge and circumvent the disposal problem have been suggested. The high calorific value of the sludge may be used in calcination of clay and manufacture of ceramic materials. This communication reports the kinetics of dehydroxylation of a kaolin clay in presence of ETP sludge. Nonisothermal methods are applied to obtain the thermal curves. Nine solid-state mechanisms are applied for analysing the data obtained in the temperature range of 450–750 °C. Random nucleation is the major process of decomposition in both the clay and clay–sludge mixture at the lower temperature range (450–600 °C). At higher temperatures (600–750 °C), the thermal decomposition of the sludge follows a three-dimensional diffusion process and occurs at the phase boundary with spherical symmetry. The thermal decomposition of the clay–sludge mixture, in the temperature range of 600–750 °C, occurs at the phase boundary with cylindrical symmetry. The kinetic parameters follow the kinetic compensation effect.

Cementitious properties of metakaolin-normal Portland cement mixture in the presence of petroleum effluent treatment plant sludge

Abstract The physicochemical characteristics of cocalcined kaolin and petroleum effluent treatment plant (ETP) sludge and its effect on the technological and hydration characteristics of cement have been presented. Conductivity measurements indicate that both the sludge ash (SA) and cocalcined kaolin–sludge mixtures in aqueous medium are reactive in nature. The rate of hydration was investigated by determining the combined water (CW) and Ca(OH) 2 content in the hydration products. The hydration products were characterized by FTIR spectrophotometric method and XRD analysis technique. The rates of hydration of cement containing cocalcined kaolin–sludge mixtures are comparatively higher than the others. Blended cements with improved technological properties may be prepared by replacing 20% cement with cocalcined kaolin–sludge mixtures containing up to 30% sludge.

Behavior of B, Cr, Se, As, Pb, Cd, and Mo present in waste leachates generated from combustion residues during the formation of ettringite

The behavior of B, Cr, Se, As, Pb, Cd, and Mo in the leachates generated from two combustion residues, coal-fired power plant fly ash and municipal solid waste incineration ash, during precipitation of ettringite is presented. Experiments also were performed using modeled waste leachates as well as controlled solutions containing all the investigated elements. Moreover, to determine the possible effect of pH, lime treatment was conducted using the waste and modeled leachates. Results indicated the removal of B, Se, and Cr from the leachates because of incorporation of their oxyanions in the ettringite structure. The removal of B could further be explained by considering the structure of ettringite and monosulfoaluminate. The removal of Pb also occurred, probably because of lime-induced precipitation of Pb(OH)2. Similarly, the removal of As was observed as a result of lime-induced precipitation of Ca3(AsO4)2 and incorporation into the ettringite structure. On the other hand, the precipitation of ettringite did not reduce the concentrations of Mo and Cd because of the complex nature of these elements in the leachates. The results also suggest that the presence of high amounts of constituents such as Cl-, an alkali metal in the solution, also affected ettringite precipitation behavior. Moreover, elemental speciations as well as the presence of other constituents in the solution affected the incorporation by ettringite.

Hydration behaviour of lime–co-calcined kaolin–petroleum effluent treatment plant sludge

Abstract Petroleum effluent treatment plant (ETP) sludge contains hydrocarbons and its ash is pozzolanic in character. The hydrocarbon may be utilized in the calcination of clay. The present communication reports on the hydration behaviour of lime–metakaolin mixtures produced in the presence of the sludge. The hydration products were characterized by using FTIR, TG, DTA and XRD methods. Use of sludge in metakaolin preparation increases the initial hydration rate and enhances the production of C–S–H or C–A–S–H gel.

Waste polyethylene terephthalate as an aggregate in concrete

This paper reports the strength behaviour of concrete containing three types of recycled polyethylene terephthalate (PET) aggregate. Results are also analysed to determine the PET-aggregates effect on the relationship between the flexural and splitting tensile strengths and compressive strength and to know whether the relationships between compressive strength and other strength characteristics given in European design codes are applicable to concrete made with PET-aggregates. The compressive strength development of concrete containing all types of PET-aggregate behaves like in conventional concrete, though the incorporation of any type of PET-aggregate significantly lowers the compressive strength of the resulting concrete. The PET-aggregate incorporation improves the toughness behaviour of the resulting concrete. This behaviour is dependent on PET-aggregates shape and is maximised for concrete containing coarse, flaky PET-aggregate. The splitting tensile and flexural strength characteristics are proportional to the loss in compressive strength of concrete containing plastic aggregates.

Physicochemical and cementitious properties of sludge from oil field effluent treatment plant

Abstract Sludge generated in the effluent treatment plants (ETPs) of oil fields contain calcite, clay and other inorganic materials as well as hydrocarbon oil. The amount of the latter is often more than the permissible level for safe disposal by landfilling. The thermoanalytical characteristics of the sludge generated in the ETP of Lakwa oil field, Assam, India were investigated by using TG, DTG, DTA, XRD, FTIR techniques and chemical methods. The lime reactivities of the sludge ash and the physical properties of blended cement containing the ash were evaluated. Decomposition of calcite starts from above 550°C and it is succeeded by several solid state reactions involving CaO and aluminosilicates forming new phases. Gehlenite (Ca 2 Al 2 SiO 7 ) has been identified as one of the products and it forms above 750°C. Sludge ash prepared at 750°C consumes considerable amount of lime but it is not suitable for preparation of blended cement.

Concrete with Recycled Aggregates in International Codes

Despite being an ancient activity, the management of waste produced in construction activities did not get much attention until the last decade. Construction and demolition waste (CDW) is not subjected to management practices as with municipal solid waste, perhaps due to the higher toxicity of the latter as compared with the former’s. Recently, rapid urban expansion, stringent environmental regulations and the scarcity of land filling areas as well as the natural resources over-exploitation led to the need of using CDW as aggregate for construction purposes.

Industrial Waste Aggregates

The aggregates typically account for 70–80 % of the concrete volume and play a substantial role in different concrete properties such as workability, strength, dimensional stability and durability. Conventional concrete consists of sand as fine aggregate and gravel, limestone or granite in various sizes and shapes as coarse aggregate.

Use of Industrial Waste as Aggregate: Properties of Concrete

As indicated in an earlier section, aggregates account for the largest part of the concrete volume and therefore play a substantial role in almost all concrete properties such as workability, strength, dimensional stability, and durability. Recently, several waste materials have been studied to be used as aggregate in concrete. The use of waste as aggregates can consume vast amounts of waste materials as this is the major component of cement mortar and concrete.