Evaluation of Calcium Aluminate Slags and Pig Irons Produced from the Smelting-Reduction of Diasporic Bauxite

This work evaluates the characteristics of calcium aluminate slag and pig iron samples obtained from the smelting of calcined and reduced diasporic bauxite ore. The study is conducted in the Pedersen process framework, which is a method to produce alumina from low-grade resources. Parameters such as the effect of crucible type, lime addition, and atmospheric conditions are studied considering the characteristics of the product pig irons and calcium aluminate slags for further uses. The behavior of the bauxite and distribution of the species between slag and metal was assessed based on the applied analytical techniques and thermodynamic calculations. Iron was reduced and separated from the slags in the presence of carbon (graphite crucible) for both the reduced and calcined bauxite. Si and Ti were mainly concentrated in the slags. Iron was separated from the slag in the absence of carbon (alumina crucible) for the H2-reduced bauxite. The results show that slags with increased lime additions are composed mainly of 5CaO.Al2O3 and CaO.Al2O3, that are considered highly leachable compounds. An optimum CaO/Al2O3 mass ratio of 1.12 was suggested. The presence of O2 and/or OH- in the furnace atmosphere will result in the formation of 12CaO.7Al2O3.

Sulphate removal technologies for the treatment of mine-impacted water

Mine-impacted water, including acid mine drainage (AMD), is a global problem. While precipitation of dissolved metals and neutralization of acidity from mine-impacted water is accomplished relatively easily with lime addition, removal of sulphate to permissible discharge limits is challenging. This paper presents a high-level comparison of four sulphate removal technologies, namely reverse osmosis, ettringite precipitation, barium carbonate addition, and biological sulphate reduction. Primarily operating costs, based on reagent and utility consumptions, are compared. Each process is shown to be subject to a unique set of constraints which might favour one over another for a specific combination of location and AMD composition. Access to and cost of reagents would be a key cost component to any of the processes studied. The total cost calculated for each process also depends on the type of effluents that are allowed to be discharged.

A Review Study: Utilization of Coir Reinforcement for Unpaved Roads

In this article, we discuss the founding of different research paper published so far using Coir across the globe in road construction. Coir is widely being used for a period of time in construction of pavements as a soil reinforcer. It is environment-friendly, biodegradable and sustainable hence does not poses any problem of disposal. The present study predominantly focuses on the utilization of coir improving the strength properties of lime balanced out sub-grade soil and then its cost benefits in designing flexible pavement for rural roads. Soil sub-grade is a key component of pavement, as they have to finally bear the burden coming over the pavement. Taking everything into account, the soil sub-grade should not be overemphasized at whatever point. The construction of streets in a large portion of the spots across the country is confronted with serious issues because of weak sub-grade soil. This Chapter includes the critical studies on the use of lime, coir and other filaments in the development of soil subgrade. The behaviour of fibre-reinforced soil and how it meets the need for lime addition and other industrial wastes has also been studied. In this article, we discuss

Responses of crop yield, apparent potassium balance, and soil potassium status to long-term fertilization and lime addition in acidic Ultisol

Soil acidification is one of the major soil degradation phenomenon in tropical and subtropical region, which cause reductions in soil fertility, particularly potassium (K), and declines in crop yield. However, it remains unclear whether and how the status of K in soils and crops changes with the application of lime to alleviate soil acidification. Six treatments of long-term experiments (started 1990) in subtropical region were carried out. Regardless of fertilization regime, lime addition markedly increased grain and straw yields compared to those yields without lime application. Lime addition also led to significant decreases in the apparent K balances compared to soils without lime application. The agronomic K efficiency and partial factor productivity of K fertilizer both significantly increased after lime application. Lime addition reduced the soil exchangeable K (EK) content and stock, while increased soil non-exchangeable K (NEK) content and stock. Redundancy analysis showed that K input, lime, pH, and exchangeable calcium all significantly affected the K in soil and crops. Path analysis showed that lime indirectly influenced soil K (EK and NEK) by directly affecting soil pH, exchangeable calcium, K uptake and apparent K balances. These results suggest that lime addition is a viable strategy for improving crop yields and K fertilizer efficiency in degraded soils caused by acidification. Lime significant increased K uptake which lead to decreased soil EK content and stock. Additional, lime also increased soil NEK content and stock which was regulated by soil pH, exchangeable calcium, and crop growth.

The extent, significance and amelioration of subsurface acidity in southern New South Wales, Australia

Soil pH is seldom uniform with depth, rather it is stratified in layers. The soil surface (0–0.02 m) commonly exhibits relatively high pH and overlies a layer of acidic soil of 0.05–0.15 m deep, termed an acidic subsurface layer. Commercial and research sampling methods that rely on depth increments of 0.1 m either fail to detect or under report the presence or magnitude of pH stratification. The occurrence of pH stratification and the presence of acidic subsurface layers may cause the extent of acidity in NSW agricultural land to be underestimated. Though the cause of pH stratification in agricultural systems is well understood, the effect on agricultural production is poorly quantified due in part to inadequate sampling depth intervals resulting in poor identification of acidic subsurface layers. Although liming remains the best method to manage acidic soil, current practices of low pH targets (pHCa 5), inadequate application rates and no or ineffective incorporation have resulted in the continued formation of acidic subsurface layers. Regular monitoring in smaller depth increments (0.05 m), higher pH targets (pHCa > 5.5) and calculation of lime rate requirements that account for application method are required to slow or halt soil degradation by subsurface acidification. If higher pH is not maintained in the topsoil, the acidification of subsurface soils will extend further into the profile and require more expensive operations that mechanically place amendments deep in the soil. Although the use of organic amendments has shown promise to enhance soil acidity amelioration with depth, the longevity of their effect is questionable. Consequently, proactive, preventative management of topsoil pH with lime addition remains the most cost-effective solution for growers.