Method for preparing lithium-aluminum adsorbent from brine with low magnesium-lithium ratio

The invention discloses a method for preparing a lithium-aluminum adsorbent from brine with a low magnesium-lithium ratio. The method comprises the following steps: carrying out coprecipitation nucleation reaction on a lithium-aluminum mixed salt solution, an inorganic alkali solution and a modifier under the condition that the pH value is 5-7 to obtain a lithium-aluminum adsorbent crystal nucleus; wherein the lithium-aluminum mixed salt solution is prepared from brine with a low magnesium-lithium ratio, and the brine with the low magnesium-lithium ratio comprises lithium-rich brine extracted by an adsorption method and/or lithium-rich brine extracted by a membrane method; the ratio of magnesium to lithium in the lithium-rich brine extracted by the adsorption method is (3-5): 1, and the ratio of magnesium to lithium in the lithium-rich brine extracted by the membrane method is (0.1-0.5): 1; and carrying out aging treatment on the lithium-aluminum adsorbent crystal nucleus to obtain the lithium-aluminum adsorb