Preparation method for iron phosphate and preparation method for lithium iron phosphate

A preparation method of iron phosphate, comprising:

• mixing pyrite cinder and a sulfite evenly in water to obtain a first mixed system;
• adding phosphoric acid and a buffer to the first mixed system to perform a leaching reaction;
• performing a first solid-liquid separation on a slurry obtained from the leaching reaction to obtain a first filtrate and a first residue;
• introducing air into the first filtrate and then performing a first stirring reaction on the first filtrate;
• performing a second solid-liquid separation on a slurry obtained from the first stirring reaction to obtain a second filtrate and a second residue;
• and
• calcining the second residue to obtain iron phosphate;
• wherein the leaching reaction is performed at a pressure of 0.25 MPa˜0.5 MPa for a time of 1 hour˜2 hours;
• a pH of a reaction system of the leaching reaction is 1.5˜3;
• the buffer comprises sodium dihydrogen phosphate and/or disodium hydrogen phosphate.