Towards a low-carbon society: A review of lithium resource availability, challenges and innovations in mining, extraction and recycling, and future perspectives

In the loose and fractured coal seam with particularly low uniaxial compressive strength (UCS), driving a roadway is extremely difficult as roof falling and wall spalling occur frequently. To address this issue, the jet grouting (JG) technique (high-pressure grout mixed with coal particles) was first introduced in this study to improve the self-supporting ability of coal mass. To evaluate the strength of the jet-grouted coal-grout composite (JG composite), the UCS evolution patterns were analyzed by preparing 405 specimens combining the influential variables of grout types, curing time, and coal to grout (C/G) ratio. Furthermore, the relationships between UCS and these influencing variables were modeled using ensemble learning methods i.e. gradient boosted regression tree (GBRT) and random forest (RF) with their hyperparameters tuned by the particle swarm optimization (PSO). The results showed that the chemical grout composite has higher short-term strength, while the cement grout composite can achieve more stable strength in the long term. The PSO-GBRT and PSO-RF models can both achieve high prediction accuracy. Also, the variable importance analysis demonstrated that the grout type and curing time should be considered carefully. This study provides a robust intelligent model for predicting UCS of JG composites, which boosts JG design in the field.

Development of ensemble learning models to evaluate the strength of coal-grout materials

Thermodynamic calculations are an essential tool for many areas of geochemistry. Thermodynamics provides a framework for the quantitative description and prediction of the solubilities and relative stabilities of different minerals, metal transport in hydrothermal fluids, and geobiochemical reactions that drive microbial metabolism and contribute to the compositional variation of proteins. Accessible and up-to-date software and databases are important for the development and reproducible application of thermodynamic models. CHNOSZ is a free package for R that has been frequently updated since its first release in 2008. The package provides an integrated set of functions to calculate the standard molal thermodynamic properties and chemical affinities of reactions. It uses the graphical capabilities of R to produce high-quality chemical activity diagrams for aqueous species and predominance diagrams including Eh-pH (Pourbaix) and logfO2-T diagrams. The extensive database utilizes the well-known revised Helgeson-Kirkham-Flowers (HKF) equations for aqueous species. Recent additions to the database include the Berman equations for minerals, the Deep Earth Water model, which extends the applicability of the HKF equations to higher pressures, and the Akinfiev-Diamond model for aqueous nonelectrolytes. The package comes with many types of documentation, including technical help pages with short code examples, longer code demos, and in-depth vignettes combining code, text and graphics, giving users a wide array of starting points for their own research. This paper provides a concise overview of the package and illustrates the new features using examples selected from the literature. Although the package does not provide a complete chemical speciation model, numerous examples from the package demonstrate the ease of reproducing selected published calculations and sometimes identifying issues with existing datasets and models.

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CHNOSZ: Thermodynamic Calculations and Diagrams for Geochemistry

In many applications such as grouting, shotcrete, and 3D concrete printing, conflicting material requirements exist between the transportation and fabrication process, as fresh materials should be pumped easily with a low stiffening rate and a high fluidity while a rapid strength gain must occur after placement. In such applications, it is therefore imperative to achieve a stiffening control of the concrete. In this paper, we discuss how the inline mixing process of an accelerator post-pumping can be used to achieve this stiffening control. We begin with a review of the mechanisms of various commonly used accelerators. This is followed by a detailed discussion on the inline mixing process of accelerators. Finally, we also point out the problems and challenges of using accelerators in these applications.

Stiffening control of cement-based materials using accelerators in inline mixing processes: Possibilities and challenges

soil-cement is a mixture produced by grouting or mixing cement with soils. This paper reviews and discusses the general classifications of grouting techniques and the suitability of their applications. The mechanical properties of soil-cement mixture and the influence of sodium silicate added are discussed. Design considerations for deep soil mixed wall (DSMW) for excavation support and vault arch for tunnelling stabilisation are presented. Parameters for the numerical analysis of soil-cement mixture are evaluated and recommended.

Soil-cement mixture properties and design considerations for reinforced excavation

Grout injection is used for sealing or strengthening the ground in order to prevent water entrance or any failure after excavation. There are many methods of grouting. Permeation grouting is one of the most common types in which the grout material is injected to the pore spaces of the ground. In grouting operations, the grout quality is important to achieve the best results. There are four main characteristics for a grout mixture including bleeding, setting time, strength, and viscosity. In this paper, we try to build some efficient grouting mixtures with different water to cement ratios considering these characteristics. The ingredients of grout mixtures built in this study are cement, water, bentonite, and some chemical additives such as sodium silicate, sodium carbonate, and triethanolamine (TEA). The grout mixtures are prepared for both of the sealing and strengthening purposes for a structural project. Effect of each above-mentioned ingredient is profoundly investigated. Since each ingredient may have positive or negative aspect, an optimization of appropriate amount of each ingredient is determined. The optimization is based on 200 grout mixture samples with different percentages of ingredients. Finally, some of these grout mixtures are chosen for the introduced project. It should be mentioned that grouting operations depend on various factors such as pressure of injection, ground structure and grain size of soils. However, quality of a grout can be helpful to make an injection easier and reasonable. For example, during the injection, a wrong estimated setting time can destroy the injected grout by washing the grout or setting early which prevents grouting. This paper tries to show some tests in easy way to achieve a desirable sample of grout.

Optimization of cement-based grouts using chemical additives

A review on methods for liberating lithium from pegmatities

Cement-based grouting has been widely used in underground coal mining to improve the overall quality of highly fractured rock masses. Due to the difficulties in obtaining characteristic specimens from highly fractured coal rocks, there are very limited laboratory studies investigating the effect of grout on the strength of coal. The purpose of this paper is to address this gap by examining the effects of grouting on fractured coal in terms of overall shear strength. Two failure modes associated with coal and grouted coal specimens have been identified. The results show the shear strength improvement of grouted coal specimens as indicated by the improvement of their peak and residual cohesion as well as friction angle when the amount of reinforcing grout increases. Linear regression models were constructed for the prediction of shear strength parameters based on grout percentages. These models can be used as a guideline for the preliminary design of pre-grouting applications.

M.R. Azadi

Papers

Optimization of cement-based grouts using chemical additives

A review on methods for liberating lithium from pegmatities

Laboratory evaluation of shear strength properties for cement-based grouted coal mass

Leaching of a polymetal gold ore and reducing cyanide consumption using cyanide-glycine solutions

Data analysis and estimation of thermodynamic properties of aqueous monovalent metal-glycinate complexes