Method for extracting lithium from salt lake brine and controlling impurity content of desorption solution

The invention discloses a method for extracting lithium from salt lake brine and controlling the impurity content of a desorption solution, which utilizes the difference of adsorption characteristics of an adsorbent on lithium and sodium, enhances the adsorption condition, improves the lithium adsorption capacity of the adsorbent, and realizes the lithium extraction of the lithium in a multi-stage countercurrent washing stage of a continuous ion exchange device loaded adsorbent in a manner of adding acid in a gradient manner. The method can effectively remove elements such as sodium, potassium, magnesium and the like which are co-adsorbed in the adsorbent while washing off tail brine entrained in the loaded adsorbent, and greatly reduces the impurity content of the desorption solution. The acid supplementing amount in each stage of washing column can be flexibly adjusted, and the amount of impurities entering desorption liquid along with carried washing liquid can be reduced by adjusting the acid supplementin