The invention relates to a method for purifying mixed salt containing
arsenic,
sodium sulfite and
sodium sulfate by redissolving and freezing, and the method comprises the following steps: redissolving the mixed salt, carrying out filtering, freezing the filtrate to precipitate
sodium sulfite crystals, carrying out filtering,
drying the separated crystals to obtain a Na2SO3 product, introducing air into the filtrate to oxidize the residual
sodium sulfite into
sodium sulfate, precipitating
arsenic, and carrying out filter pressing to separate As2S5 filter residues and filtrate, performing pyrogenic process on As2S5 filter residues to obtain an As2O3 product, evaporating and concentrating filtrate to
supersaturation, carrying out cooling to separate out Na2SO4 crystals, carrying out centrifuging, and
drying the obtained crystals to obtain a Na2SO4 product. According to the method, the mixed salt can be separated and enriched at a lower production cost, so that the mixed salt which cannot be directly utilized generates market values according to respective contents, and more importantly, the harmful substance
arsenic with lower content can be enriched at a
high rate to form a high-quality
arsenic trioxide product, thereby facilitating market sale and development, and achieving the harmless and resourceful treatment on the environment-friendly strictly-controlled arsenic.