EXTRACTION SYSTEM FOR SEPARATING CALCIUM AND EXTRACTING LITHIUM FROM CALCIUM-CONTAINING BRINE BY USING SECONDARY AMIDE/ALKANE COMPOSITE SOLVENT, EXTRACTION METHOD, AND APPLICATION THEREOF

摘要

An extraction system for separating calcium and extracting lithium from calcium-containing brine by using a secondary amide/alkane composite solvent, an extraction method, and an application thereof. The extraction system contains a secondary amide and an alkane which are composed of a single compound or a mixture of two or more compounds. The total number of carbon atoms in molecules is 12-18 and 9-18 respectively, and the freezing point of the extraction system is less than 0°C. In the case that the volume ratio of an organic phase to a brine phase is 1-10:1, the density of brine is 1.30-1.56 g/cm³, the pH value of brine is 1-7, and the temperature is 0-50℃, single-stage or multi-stage countercurrent extraction is performed, back-extraction is performed to obtain a low-calcium-lithium ratio water phase, and concentration, impurity removal and preparation are performed to obtain lithium chloride, lithium carbonate and lithium hydroxide respectively. The present invention has the following good effects: the secondary amide extraction agent has a simple molecular structure and is easy to produce, and the alkane improves the properties, such as viscosity, of a composite solvent; the multi-stage extraction rate of Li⁺ is high, the lithium calcium separation coefficient is large, and back-extraction with water greatly reduces the consumption of acid and alkali; the extraction and separation process is short, the extraction system dissolution loss is small, and the present invention is suitable for oilfield brine development.