1) Leaching: Ammonia-ammonium sulfate solution for leaching with an aqueous ammonia concentration of 5. 5~7. Omol/L, ammonium sulfate molar concentration of 0~lmol/L (adjusted sulfate concentration according to product type) , at a temperature of 20~50 ° C, leaching for 3h~9h, the final infusion solution is used in the next step;