The extraction system contains secondary amides and alkyl alcohols which are separately used as the extractants for extracting lithium and boron and consist of a single compound or a mixture of two or more compounds, and the total number of carbon atoms in their molecules are 1218 and 820 respectively; the extraction system has a freezing point less than 0 C. With a volume ratio of an organic phase and a brine phase being 110:1, at a brine density of 1.251.38 g/cm.sup.3, at a brine pH value of 07 and at a temperature of 050 C., a single-stage or multi-stage countercurrent extraction and a stripping are conducted to obtain a water phase with a low magnesium-lithium ratio, which is subjected to concentration, impurity removal and preparation to get lithium chloride, lithium carbonate, lithium hydroxide and boric acid respectively. Water is used for stripping, greatly reducing the consumption of acid and base.

A process and an installation wherein a ternary system including an aqueous acidic solution, an organic solvent not miscible with water and a thermosensitive hydrotropic agent is used to selectively extract tantalum and optionally niobium by cycling extraction between low-temperature single-phase and high temperature two phase regions in the ternary phase prism far from the critical point.