Abstract: There is described a process which comprises adjusting on the one hand the flow rates of a circulating mixture relative to a base flow rate according to very specific specifications, and on the other hand so adjusting the reaction conditions in succeeding reaction zones as to obtain a production phosphoric acid with a P.sub.2 O.sub.5 concentration between 33 and 52%, and a H.sub.2 SO.sub.4 concentration between 0.25 and 2.5%, and calcium sulphate in the form of dihydrate, hemihydrate, anhydrite or a mixture of at least two said crystalline forms.

Abstract: Vacuum rotary filter with horizontal filtering plane comprising a distributor consisting of a distributor part, a collector part and a gas separation chamber. The collector part (110) consists of a single vat divided into three compartments (139, 140, 141, respectively), for the mother water, the first washing liquid and the second washing liquid. The compartments may be interconnected so as to enable a fluid circulation in an imposed direction. The collector part also comprises a sector for annex operations and presuction.

Abstract: The present invention provides a continuous method for preparing phosphoric acid and calcium sulphate by reacting calcium phosphate with a mixture of sulphuric acid and phosphoric acid. Our method uses at least three successive crystallization steps: a first step of reacting the phosphate with the mixture of phosphoric and sulphuric acids and forming a-hemihydrate calcium sulphate, a second step of recrystallizing the a-hemihydrate into dihydrate and a third step of transforming the dehydrated calcium sulfate into a hemihydrate or anhydrite II or a mixture of the two. Where desired recycling of the products from the above steps can be used for increasing the efficiency of the above method.

Abstract: A cell filter having a series of filtering cells and a distributor for collecting and adjusting the distribution of fluids passing through the cell filtering surface. Each cell has a planar filtering bed composed of a filtering cloth bearing on a rigid apertured support. Fluid passes through the cloth onto the cell bottom which slants toward a drain channel. The drain channel slants toward a discharge duct connected to a distributor. Guide members in the distributor fractionate, divide, and direct the fluid flowing towards the discharge duct into two parallel adjacent streams. The guide members are a series of baffle plates, located along the top length of the drain channel. The baffle plates are slanted, the plate farthest from the low end of the drain channel having the steepest slant.

Abstract: A wet phosphoric acid production process comprising the attack on phosphate rock by sulfuric acid and phosphoric acid utilizing a vacuum cooling and a recirculation of the reaction slurry. The flow rates of the materials within the system are maintained at a level, relative to the rate of withdrawal of the slurry from the system, of between 300% and 4000% for the cyclic flow, between 2000% and 4000% for the vacuum cooling flow and between 500% and 2200% for the local agitation flow. Control of the flow rates according to factors including the rock analysis allows maximization of the yield of H.sub.3 PO.sub.4.

Abstract: The present invention relates to a process for treating residues from a primary leaching of ferriferous zinc ores by sulphuric acid, with a view to recover a leadbearing by-product, such process comprising a secondary leaching of said residues, by sulphuric acid, within several countercurrent stages, at a temperature comprised between 85.degree. and 100.degree. C., the solid residues of the successive stages being circulated from the first to the last stage, the residue of this last stage being the said lead bearing by-product, whereas the various solutions separated from the second to the last stage are each recycled within the leaching operation of the respectively foregoing stage, and the dual zinc and iron sulphates solution, as separated from the first stage, being the principal product of the treatment.

Abstract: A cell filter having a collecting part divided into chambers and compartments and provided with cavities. Each compartment is provided on the one hand at the bottom thereof with at least one liquid-discharge outlet lying substantially below that level where the cavities open and on the other hand, above the liquid top level, with at least one passageway towards a gas-sucking device in such a way as to suck the gases while causing the gases and liquids to separate and go along different paths inside the compartments, means being provided to return to the original compartment those liquids which might have entered the passageways so as on the one hand, obtain at the distributor outlet, liquid-free gases and on the other hand, collect through the discharge openings only liquids which are substantially free from undissolved gases.