Process for the recovery of synthetic anhydrite

Claim 1

A PROCESS FOR RECOVERING SYNTHETIC ANHYDRITGE, FOR USE AS AN INORGANIC BUILDING MATERIAL BINDER, FROM THE HOT CALCIUM SULFATE SLUDGE PRODUCED BY THE CONTINUOUS PROCESS OF MANUFACTURING HYDROFLUORIC ACID THROUGH THE ACTION OF CONCENTRATED SULFURIC ACID ON CALCIUM FLUORIDE, THE SAID SLUDGE CONSISTING SUBSTANTIALLY ENTIRELY OF A MAJOR PROPORTION OF ANHYDROUS CALCIUM SULFATE AND A MINOR PROPORTION OF SUBSTANTIALLY ANHYDROUS SULFURIC ACID, COMPRISING MIXING WITH THE SLUDGE AT A TEMPERATURE OF MORE THAN 100*C. WHILE SUBSTANTIALLY PREVENTING ACCESS TO THE RESIDUE OF MOISTURE FROM THE AIR OR OTHER SOURCES, A DRY, BASIC NEUTRALIZING MATERIAL SELECTED FROM THE GROUP CONSISTING OF CALCIUM OXIDE, CALCIUM HYDROXIDE AND CALCIUM CARBONATE IN AN AMOUNT SUFFICIENT TO NEUTRALIZE THE SULFURIC ACID, AND ALLOWING THE NEUTRALIZATION TO PROCEED TO COMPLETION, THE TEMPERATURE OF THE SLUDGE AT THE BEGINNING OF THE NEUTRALIZATION REACTION NOT EXCEEDING 150*C.