Method for reclaiming gypsum from wasted gypsum boards

A method for reclaiming gypsum from wasted gypsum boards comprising:

• crushing and heating wasted gypsum boards to produce semi-hydrated gypsum and/or anhydrous type III gypsum;
• mixing said semi-hydrated gypsum and/or anhydrous type Ill gypsum with gypsum slurry;
• solid/liquid separating the gypsum slurry by a filtration device into gypsum particles and filtrate which has passed through a filter cloth of the filtration device such that a concentration of suspended solid in the filtrate that has passed through the filter cloth and comprises gypsum granules and inorganic impurities derived from the wasted gypsum boards is made 1000 to 8000 mass ppm;
• returning the filtrate into the gypsum slurry;
• sieving the gypsum slurry by at least a first stage vibrating sieve and a second stage vibrating sieve before the solid/liquid separation;
• supplying the gypsum slurry and under-sieve component of the second stage vibrating sieve to an inlet of the first stage vibrating sieve, and supplying the under-sieve component of the first stage vibrating sieve to the filtration device;
• and
• supplying upper-sieve component of the first stage vibrating sieve and washing water to an inlet of the second stage vibrating sieve, returning the under-sieve component of the second stage vibrating sieve to the inlet of the first stage vibrating sieve, and reclaiming paper dust from the upper-sieve component of the second stage vibrating sieve.