A process for the recovery of sodium sulfate from water, in particular from water deriving from a silica manufacturing process.

A method for the production of potassium sulphate comprising contacting an aqueous potassium- and sulphate-containing composition with magnesium chloride (MgCl.sub.2), thereby obtaining a composition comprising kainite; optionally concentrating the kainite from the composition; reacting the kainite with magnesium sulphate (MgSO.sub.4) and potassium sulphate (K.sub.2SO.sub.4) so as to convert the kainite into leonite (K.sub.2SO.sub.4.MgSO.sub.4.4H.sub.2O); optionally contacting the leonite with water to remove excess MgSO.sub.4; and contacting the leonite with water so as to leach the MgSO.sub.4, contained in the leonite, and to at least substantially selectively precipitate potassium sulphate (K.sub.2SO.sub.4). The method can be operated at higher temperatures, in particular, at temperatures above 35 C., and does not require a cooling step at 20 to 25 C. The method produces potassium sulphate with a low amount of chloride.

A method for the production of potassium sulphate comprising contacting an aqueous potassium- and sulphate-containing composition with magnesium chloride (MgCl.sub.2), thereby obtaining a composition comprising kainite; optionally concentrating the kainite from the composition; reacting the kainite with magnesium sulphate (MgSO.sub.4) and potassium sulphate (K.sub.2SO.sub.4) so as to convert the kainite into leonite (K.sub.2SO.sub.4.MgSO.sub.4.4H.sub.2O); optionally contacting the leonite with water to remove excess MgSO.sub.4; and contacting the leonite with water so as to leach the MgSO.sub.4, contained in the leonite, and to at least substantially selectively precipitate potassium sulphate (K.sub.2SO.sub.4). The method can be operated at higher temperatures, in particular, at temperatures above 35 C., and does not require a cooling step at 20 to 25 C. The method produces potassium sulphate with a low amount of chloride.

The present invention relates to a process for producing sodium sulphate from phosphogypsum, comprising: a step (101) of lixiviation of phosphogypsum by means of a basic solution so as to obtain a sodium sulphate solution (S) containing metal impurities, said basic solution comprising a chelating agent suitable for forming complexes with at least one part of said metal impurities, at least one first step (103, 104) of filtration of the sodium sulphate solution by a nanofiltration membrane (NF1, NF2), so as to form a concentrate (C1, C2) containing said complexes and a permeate (P1, P2), a step (105) of evaporation of the permeate (P1, P2) so as to form anhydrous sodium sulphate.

The present invention relates to a process for producing sodium sulphate from phosphogypsum, comprising: a step (101) of lixiviation of phosphogypsum by means of a basic solution so as to obtain a sodium sulphate solution (S) containing metal impurities, said basic solution comprising a chelating agent suitable for forming complexes with at least one part of said metal impurities, at least one first step (103, 104) of filtration of the sodium sulphate solution by a nanofiltration membrane (NF1, NF2), so as to form a concentrate (C1, C2) containing said complexes and a permeate (P1, P2), a step (105) of evaporation of the permeate (P1, P2) so as to form anhydrous sodium sulphate.

There are provided methods for the production of potassium sulphate. The methods comprise contacting an aqueous potassium- and sulphate-containing composition with magnesium chloride (MgCl.sub.2), thereby obtaining a composition comprising kainite; optionally concentrating the kainite from the composition and reducing or removing halite therefrom; reacting the kainite with magnesium sulphate (MgSO.sub.4) and potassium sulphate (K.sub.2SO.sub.4) so as to convert the kainite into leonite (K.sub.2SO.sub.4.MgSO.sub.4.4H.sub.2O); optionally contacting the leonite with water to remove excess MgSO.sub.4; and contacting the leonite with water so as to leach the MgSO.sub.4, contained in the leonite, and to at least substantially selectively precipitate potassium sulphate (K.sub.2SO.sub.4), further involving a process brine sulphate control step, based on bloedite precipitation, to control the overall level of sulphate in the method and further comprising a step for the substantially complete reduction or removal of halite from the flotation concentrate, accompanied by an additional precipitation of kainite, thus also increasing the overall recovery of kainite in the process. The method according to the invention can be operated at higher temperatures, in particular at temperatures above 35 C. and does not require a cooling step at 20 to 25 C. The method produces potassium sulphate with a low amount of chloride.

Provided is a leaching-seepage process of sodium sulfate in a thenardite tailings stack. The process includes the following steps: step 1, providing a mud reserve pit next to the thenardite tailings stack, and ditching a drainage ditch next to a bottom of the thenardite tailings stack; step 2, ditching a leaching pit on the thenardite tailings stack, injecting water, and letting the water stand to leach thenardite tailings; step 3, leaching the thenardite tailings with the water, so that a percolating fluid gradually flows out from the bottom of the thenardite tailings stack; step 4, flushing the bottom of the thenardite tailings stack with a spray gun, to mix the percolating fluid with mud to flow into the drainage ditch; and step 5, settling naturally in the mud reserve pit, and extracting a supernatant from the mud reserve pit by a water pump to obtain refined Glauber's salt water.

Provided is a leaching-seepage process of sodium sulfate in a thenardite tailings stack. The process includes the following steps: step 1, providing a mud reserve pit next to the thenardite tailings stack, and ditching a drainage ditch next to a bottom of the thenardite tailings stack; step 2, ditching a leaching pit on the thenardite tailings stack, injecting water, and letting the water stand to leach thenardite tailings; step 3, leaching the thenardite tailings with the water, so that a percolating fluid gradually flows out from the bottom of the thenardite tailings stack; step 4, flushing the bottom of the thenardite tailings stack with a spray gun, to mix the percolating fluid with mud to flow into the drainage ditch; and step 5, settling naturally in the mud reserve pit, and extracting a supernatant from the mud reserve pit by a water pump to obtain refined Glauber's salt water.

The invention relates to a method for producing for producing soluble potassium sulfate by recrystallization of crude potassium sulfate wherein the crude potassium sulfate contains an amount of potassium, calculated as K.sub.2O of about 15 wt % or higher preferably about 40 wt % or higher and has either more than about 0.07 wt % insoluble material, and/or a dissolution speed wherein at 3 min dissolution of 100 gram product in 1 L cold water (20 C.), without stirring the amount of dissolved potassium sulfate of less than about 90% and/or a pH of about 6 or higher as a 1% dissolved crude potassium sulfate, wherein the method comprises the following steps: crude potassium sulfate is dissolved, the dissolved potassium sulfate is subjected to a solid material removal step, potassium sulfate is crystallized, while optionally an acid is provided before, during or after the crystallization step of the potassium sulfate and whereafter the obtained potassium sulfate is separated and dried, wherein the particle size of the crystalline material is controlled to be within the ranges provided, optionally with sieving and/or grinding, preferably by sieving, such that the resulting potassium sulfate crystalline material conforms with the following characteristics: the amount of insoluble material is less than about 0.05 wt %, a 1 wt % solution of the potassium sulfate has a pH below about 6, and/or 1 pH unit lower than the pH of the crude potassium sulfate, the fraction obtained after crystallization has an average particle size within the following parameters: (i) d90<about 0.6 mm, (ii) d10>about 0.02 mm, and (iii) dust amounts to about 0.4 wt % or less, whereby the potassium sulfate contains more than 51% potassium, calculated as K.sub.2O.

The invention relates to a method for producing for producing soluble potassium sulfate by recrystallization of crude potassium sulfate wherein the crude potassium sulfate contains an amount of potassium, calculated as K.sub.2O of about 15 wt % or higher preferably about 40 wt % or higher and has either more than about 0.07 wt % insoluble material, and/or a dissolution speed wherein at 3 min dissolution of 100 gram product in 1 L cold water (20 C.), without stirring the amount of dissolved potassium sulfate of less than about 90% and/or a pH of about 6 or higher as a 1% dissolved crude potassium sulfate, wherein the method comprises the following steps: crude potassium sulfate is dissolved, the dissolved potassium sulfate is subjected to a solid material removal step, potassium sulfate is crystallized, while optionally an acid is provided before, during or after the crystallization step of the potassium sulfate and whereafter the obtained potassium sulfate is separated and dried, wherein the particle size of the crystalline material is controlled to be within the ranges provided, optionally with sieving and/or grinding, preferably by sieving, such that the resulting potassium sulfate crystalline material conforms with the following characteristics: the amount of insoluble material is less than about 0.05 wt %, a 1 wt % solution of the potassium sulfate has a pH below about 6, and/or 1 pH unit lower than the pH of the crude potassium sulfate, the fraction obtained after crystallization has an average particle size within the following parameters: (i) d90<about 0.6 mm, (ii) d10>about 0.02 mm, and (iii) dust amounts to about 0.4 wt % or less, whereby the potassium sulfate contains more than 51% potassium, calculated as K.sub.2O.