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: The relative concentration of opaque and translucent ore particles is determined by illuminating a falling stream of particles with a source of backlighting which provides a diffused background light source for detecting opaque particles and a relatively brighter light source for further illuminating translucent particles. Scanning a captured image of the falling particle stream for light and dark light images relative to the background light permits the relative concentration of opaque and translucent particles to be determined. The method is particularly useful for beneficiated composite phosphate ores containing desirable opaque phosphate particles and undesired translucent quartz particles.

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

Abstract: The present process stabilizes merchant acid from bottoms solutions against post-precipitation by heating the acid to a temperature of at least about 180.degree. F. for about 12 to about 48 hours. The stabilized acid product exhibits less than about 1 wt % solids precipitation after even 14 days of standing at about 70.degree. F.

Abstract: A method for defluorinating wet process phosphoric acid. Phosphatic waste clay from phosphate rock beneficiation is mixed with the wet process phosphoric acid. The mixture is heated for a time sufficient to remove fluorine from the acid as gaseous silicon tetrafluoride. Phosphate is liberated from the phosphatic waste clay and thus is recovered in the defluorinated wet process phosphoric acid.

Abstract: This invention is directed to an improved froth flotation separation for beneficiating phosphate containing ores wherein an ore is preliminarily conditioned with an anionic agent and then subjected to froth flotation separation to concentrate the phosphate containing fraction. The improvement comprises the addition of sodium silicate near the end of the conditioning step before the beginning of the froth flotation.

Abstract: A method of recovering HF from an aqueous solution containing NH.sub.4 F and HF is provided. The solution is contacted with a water-immiscible, amine-containing extractant which extracts HF in preference to NH.sub.4 F. The HF:NH.sub.4 F molar ratio of the solution, the amine, the concentration of the amine in the extractant and the contact temperature are selected so as to form an HF-loaded organic liquid phase having an HF:amine molar ratio of at least about 1.2. The extractant is preferably selected from amines, amine-HF complexes, quaternary amine fluorides and mixtures thereof with inert organic diluents. After equilibration, the HF-loaded amine is separated from the solution and HF is stripped therefrom in an amount sufficient to lower the HF:amine molar ratio by at least about 0.2.