Method for preparing ammonium metavanadate from slag containing vanadium, phosphorus and arsenic

The invention discloses a method for preparing ammonium metavanadate from slag containing vanadium, phosphorus and arsenic. The method comprises the following steps that firstly, the phosphorus and arsenic slag is dissolved in water according to the solid-liquid mass ratio of 1.0: (2.0-3.0), and an aqueous solution A is prepared; step 2, adding sulfuric acid into the aqueous solution A to react to generate a precipitate, controlling the pH value of the solution at 8.0-9.0, and filtering the precipitate to obtain an aqueous solution B; 3, adding ammonium salt into the aqueous solution B, keeping the temperature of the solution at 40-60 DEG C, stirring for reaction, aging, and filtering to obtain wet ammonium metavanadate and an aqueous solution C; 4, magnesium salt or calcium salt is added into the water solution C, phosphorus and arsenic in the solution are filtered out in a precipitation mode after reaction, and meanwhile a water solution D is obtained; and 5, adding deionized water into the wet ammonium met