Abstract: In the manufacture of phosphoric acid from ore, the typical ore comprises minerals containing phosphorus and calcium along with varied amounts of other elements. Certain ores have substantial iron content which needs to be removed in order to produce quality phosphoric acid product. An improved method and associated chemical processing plant are disclosed for removing this iron. The method involves both reducing and adding oxalic acid to wet process phosphoric acid produced using an otherwise conventional manufacturing process. Iron oxalate precipitate is created which can then conveniently be separated therefrom.

Abstract: In the manufacture of phosphoric acid from ore, the typical ore comprises minerals containing phosphorus and calcium along with varied amounts of other elements. Certain ores have substantial iron content which needs to be removed in order to produce quality phosphoric acid product. An improved method and associated chemical processing plant are disclosed for removing this iron. The method involves both reducing and adding oxalic acid to wet process phosphoric acid produced using an otherwise conventional manufacturing process. Iron oxalate precipitate is created which can then conveniently be separated therefrom.

Abstract: Maximum throughput of a wet process phosphoric acid plant at a fixed recovery can be obtained by controlling the filter feed to give a desired specific gravity of the filtrate from the last washing of the gypsum cake. The filtrate from the last washing of the gypsum cake also is called the first pass filtrate. The specific gravity of this first pass filtrate provides an indication of the overall filter efficiency and the loss of water-soluble phosphoric acid to the gypsum waste stream. The specific gravity of the first pass filtrate is controlled by adjusting the rate at which product slurry from the attack tank is fed to the filter. This product slurry feed rate is affected by the mechanical performance of the filter and the filterability of the gypsum crystals, which, in turn, is affected by operating conditions in the attack tank. Therefore, the feed rates of phosphate rock, sulfuric acid, and water, are controlled to produce the desired attack tank operating conditions and to maintain attack tank level.

Abstract: An improved automatic control system for controlling a phosphoric acid plant in order to maximize recovery of phosphoric acid which includes a programmable computer, a rock flow control and measurement device for controlling and measuring the rock mass flow rate, an acid flow control and measurement device for measuring and controlling the sulfuric acid feed rate, wherein the computer is programmed to calculate the total amount of sulfuric acid added to the reactor, calculate the total amount of rock added to the reactor, over the time interval, calculate a new sulfuric acid feed point to make excess sulfate resulting from reaction of incoming acid and rock to have a predetermined excess sulfate, wherein the predetermined excess sulfate causes the phosphoric acid plant to operate at the maximum efficiency, calculate a number of gallons of sulfuric acid to be added or subtracted to the reactor to correct the excess sulfate of material already in the reactor, and to generate control signals to cause said sulfur

Abstract: A method for controlling the phosphoric acid product concentration in a continuous phosphoric acid recovery process comprising supplying a constant feed stream of phosphate ore to an attack tank wherein the phosphate ore is subjected to attack by sulfuric and phosphoric acids to produce a slurry comprising an aqueous phosphoric acid solution and calcium sulfate, filtering the slurry to form aqueous phosphoric acid and calcium sulfate filter cake, rinsing said filter cake with water, and adding said rinse water to the attack tank, calculating a first amount of water required to maintain a desired concentration of phosphoric acid in the slurry, said desired concentration calculated based on the concentration of phosphate ore in the feed stream and the filterability of the filter cake, determining the total actual amount of water added to the attack tank, and adjusting the amount of rinse water so that the amount of water added to the attack tank is sufficient to maintain the desired concentration of phosphoric