A process for producing hydrogen chloride and potassium sulphate based salts TECHNICAL FIELD

[001] The present invention relates to a low temperature, continuous fine grinding process referred to as the HYP AS process for producing hydrogen chloride and one or more potassium sulphate based salts such as potassium hydrogen sulphate, potassium ammonium sulphate, potassium magnesium sulphate, potassium magnesium/calcium sulphates, potassium calcium sulphate, potassium sulphate and mixtures thereof.

BACKGROUND

[002] Potassium sulphate based salts are primarily used in the agricultural fertiliser industry. Potassium chloride is derived from natural salt deposits but is unsuitable for some crops which are chloride intolerant. In addition, chloride can contribute to undesirable soil salinity especially in places like Australia. Potassium sulphate based fertilizers are about 30% more expensive than potassium chloride due to increased processing and extraction costs. The potassium sulphate based salts are more environmentally friendly than potassium chloride and mixed potassium sulphate based salts can also serve as a source of sulphur, nitrogen and magnesium which are essential nutrients for crops.

[003] Hydrogen chloride is used in a range of industrial applications. It is traditionally produced by the Chlor Alkali process which is tied to caustic soda and chlorine production. Various chemical processes produce hydrogen chloride as a by-product, but several of these have become obsolete. There is currently a world imbalance in the supply of hydrogen chloride due to increasing demands from the mineral and oil extraction industries. In light of the shortage of hydrogen chloride and the need for potassium sulphate based salts, there remains a need for a process that provides a less energy intensive, cleaner, integrated and more economical route than the complex processes that currently exist.

SUMMARY OF THE INVENTION

[004] According to one aspect of the present invention there is provided a process for producing hydrogen chloride and one or more potassium sulphate based salts, comprising the steps of: (i) continuously fine grinding potassium chloride and sulfuric acid at a temperature of between approximately 0°C to approximately 100°C to produce hydrogen chloride and a composition comprising potassium hydrogen sulphate;

(ii) further continuously fine grinding the potassium chloride and the

composition comprising potassium hydrogen sulphate of step (i) at a temperature of between approximately 0°C to approximately 100°C to produce hydrogen chloride and a composition comprising potassium sulphate. [005] The composition comprising potassium sulphate of step (ii) can optionally undergo further continuous fine grinding in the presence of one or more neutralizing agents in order to neutralize any residual acidity at a temperature of between approximately 0°C to approximately 100°C to provide a composition comprising one or more potassium sulphate based salts such as potassium ammonium sulphate (KNH ₄ SO ₄ ), potassium magnesium sulphate (K ₂ Mg(S0 ) ₂ ), potassium magnesium/calcium sulphates (K ₂ Ca/Mg(S0 ₄ ) ₂ ), potassium calcium sulphate (K2Ca(S0 ₄ )2), potassium sulphate (K ₂ SO ₄ ) or mixtures thereof depending on the neutralizing agent(s) used.

[006] Alternatively, the composition comprising potassium sulphate of step (ii) can optionally undergo further continuous fine grinding or be mixed with one or more balancing agents in order to balance any residual acidity at a temperature of between approximately 0°C to approximately 100°C to provide a composition comprising potassium sulphate and the one or more balancing agents.

[007] It is also possible that the composition comprising potassium sulphate of step (ii) can be divided into two or more portions and one or more of the portions undergoes either:

(a) further continuous fine grinding in the presence of one or more

neutralizing agents in order to neutralize any residual acidity at a temperature of between approximately 0°C to approximately 100°C to provide a composition comprising one or more potassium sulphate based salts; or

(b) further continuous fine grinding or mixing with one or more balancing agents in order to balance any residual acidity at a temperature of between approximately 0°Cto approximately 100°C to provide a composition comprising potassium sulphate and the one or more balancing agents.

[008] Step (ii) of the process can alternatively be replaced by a step in which the composition comprising potassium hydrogen sulphate of step (i) undergoes further continuous fine grinding in the presence of one or more neutralizing agents at a temperature of between approximately 0°C to approximately 100°C to provide a composition comprising one or more potassium sulphate based salts. [009] Alternatively step (ii) of the process can be replaced by a step in which the composition comprising potassium hydrogen sulphate of step (i) undergoes further continuous fine grinding or mixing with one or more balancing agents at a temperature of between approximately 0°C to approximately 100°C to provide a composition comprising potassium hydrogen sulphate and the one or more balancing agents.

[010] Step (ii) can also replaced by a step of dividing the composition comprising potassium hydrogen sulphate of step (i) into two or more portions and either: (a) further continuously fine grinding one or more of the portions in the presence of one or more neutralizing agents at a temperature of between approximately 0°C to approximately 100°C to provide a composition comprising one or more potassium sulphate based salts; or

(b) further continuously fine grinding or mixing one or more of the

portions with one or more balancing agents at a temperature of between approximately 0°C to approximately 100°C to provide a composition comprising potassium hydrogen sulphate and the one or more balancing agents.

BRIEF DESCRIPTION OF THE FIGURES

[Oi l] Figure 1 shows a generalised process flow sheet for the processes described herein.

DETAILED DESRIPTION

[012] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as

"comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. For example, the phrase "a composition comprising potassium hydrogen sulphate of step (i)" may include only potassium hydrogen sulphate or the composition may include any one or more of the following: potassium hydrogen sulphate, potassium chloride and/or hydrogen chloride depending on the extent to which the reactions of the process have gone to completion. The phrase "a composition comprising potassium sulphate of step (ii)" may include only potassium sulphate or the composition may include any one or more of the following: potassium sulphate, potassium hydrogen sulphate, potassium chloride and/or hydrogen chloride depending on the extent to which the reactions of the process have gone to completion. [013] Documents referred to within this specification are included herein in their entirety by way of reference.

[014] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

[015] As mentioned above, in one broad aspect this invention relates to a low temperature, continuous fine grinding process for producing hydrogen chloride and one or more potassium sulphate based salts. The phrase "potassium sulphate based salts" is intended to include potassium hydrogen sulphate (KHSO ₄ ), potassium ammonium sulphate (KNH ₄ SO ₄ ), potassium magnesium sulphate (K ₂ Mg(S0 ₄ ) ₂ ), potassium magnesium/calcium sulphates (K ₂ Ca/Mg(SC>4) ₂ ), potassium calcium sulphate (K ₂ Ca(SC>4) ₂ ), potassium sulphate (K ₂ SC>4) and mixtures thereof. The phrase "potassium sulphate based salts" is also intended to include any inorganic salt that includes at least one potassium cation, K ⁺ , and for which the sum of the charges of one or more cations such as, but not limited to, H*, K ⁺ , NH ₄ ⁺ , Mg ²⁺ , Ca ²⁺ of the inorganic salt is balanced by the charge of one or more sulphate (SO ₄ ) anions to provide an inorganic salt with a net overall charge of zero. Mixtures of such inorganic salts are also included in the phrase "potassium sulphate based salts".

[016] It is understood that the terms "sulphate" and "sulfate" are interchangeable as are the terms "sulphuric" and "sulfuric".

[017] As used herein, the phrase "low temperature" is taken to mean temperatures in the range of approximately 0°C to approximately 100°C. Preferably, the temperature range is from approximately 15 to approximately 40°C. The specified temperature ranges can apply to each of the three stages of the process described herein. It should be understood that the temperature used for one stage of the process may differ from the temperature used for another stage of the process. It is also possible that the temperature of each stage of the process can be the same. Further, each stage of the process described herein can be carried out without the need for an external source of heat.

[018] As used herein, the term "fine grinding" or "finely ground" refers to a reduction in particle size of a solid material, including crystalline salts, to achieve a particle size distribution wherein 80% -100% of the particles are less than 50 microns in diameter and 0-20% are less than or equal to 5 microns in diameter. Preferably, 90% -99% of the particles are less than 50 microns in diameter and 1- 10% are less than or equal to 5 microns in diameter. More preferably, 95% -99% of the particles are less than 50 microns in diameter and 1 -5% are less than or equal to 5 microns in diameter. Most preferably, 95% of the particles are less than 50 microns in diameter and 5% are less than or equal to 5 microns in diameter.

[019] As used herein, the term "continuous fine grinding" refers to the "fine grinding" of one or more solid reactants that is continued without interruption during each stage of the process described herein. The solid reactant or solid reactants are finely ground until such time that the anticipated reaction between the solid reactant(s) with the other reactant(s), that may or may not be solid, is at least 80% complete. More preferably, the reaction between the reactants is between 90% -99% complete. The extent to which the reaction has proceeded to completion can, for example, be determined by monitoring the rate and quantity of HC1 evolution.

[020] Fine grinding can be interrupted between each stage of the process or it can be continued during the duration of all stages of the process. For example, fine grinding can occur throughout ongoing chemical reactions such as the conversion of potassium chloride to potassium hydrogen sulphate, or the conversion of potassium hydrogen sulphate to one or more potassium sulphate based salts such as potassium sulphate, potassium ammonium sulphate, potassium magnesium sulphate, potassium calcium sulphate and potassium magnesium-calcium sulphates. The chemical conversion that occurs during the first and second stage of the process and the optional third stage of the process, as described herein, can occur as a batch or continuous processing operation depending upon plant design. [021] As used herein, the term "fine grinding equipment" refers to any mill, container, vessel, equipment, device or combinations of these types in which solid materials such as potassium chloride and potassium sulphate based salts and any solid neutralizing agent can be reduced to a particle size distribution as previously defined.

[022] As used herein, the term "solid material" or "solid materials" refers to a crystalline, semi-crystalline or non-crystalline inorganic compound or salt that is in a solid state in the process.

[023] As used herein, the term "acidic material" refers to a composition that includes one or more acidic components such as, but not limited to, potassium hydrogen sulphate, hydrogen chloride and/or sulphuric acid.

[024] As used herein, any reference to "neutralizing agent" refers to a chemical agent which neutralizes any acidity of the acidic material resulting from Stage 1 or Stage 2 of the process. This may require introduction of water, at an amount of, for example, 5 to 10 % w/w of the total mass of the reactants during the neutralization process. Examples of neutralizing agents can include, but are not limited to, one or more of the following: ammonia, ammonium hydroxide, magnesium oxide, magnesium hydroxide, magnesium carbonate, dolomite (magnesium calcium carbonate), lime or calcium carbonate. [025] As used herein, any reference to a "balancing", "balance agent" or

"balancing agent" is taken to mean an agent or a combination of agents that can be mixed or blended with an acidic material to provide sufficient alkalinity to neutralize the acidity. Neutralization of the acidity by the "balancing agent" will only be achieved when the mixed or blended acidic material and "balancing agent" are exposed to sufficient liquid water or water vapour. This may be either as part of a later processing stage, simple storage or when used by the ultimate customer in his end application. Examples of balancing agents can include, but are not limited to, one or more of the following: magnesium oxide, magnesium carbonate, dolomite (magnesium calcium carbonate), lime or calcium carbonate.

[026] As used herein, the term "pneumatic system and classifier" refers to gas transport systems which convey fine solids to a classifier which segregates a finer particle size range of solids from a coarser particle size range of solids. Some of the coarser solids may be returned to the fine grinding equipment for further size reduction. These types of pneumatic systems and classifiers that are concerned with particle size reduction are known in the art.

[027] As used herein, the term "free flowing" means at least 80% or more of the solid materials within the fine grinding equipment are capable of moving and mixing in any solid handling equipment when in operation. It is preferred that the solid materials do not bind together into agglomerates that can be, for example, 5- 50 mm in diameter. Unlike the finer salts, the agglomerates will not likely flow and fine grind in the equipment. Consequently, the reactants forming part of the agglomerates may react only slowly or not be able to react until the granular material is finely ground to expose new salt surfaces enabling a reaction to occur. As used herein, the term "granular" or "granulates" means agglomerates of 5 to 50 mm in diameter which are difficult or too large to fine grind in the fine grinding equipment and may need to be processed in coarser grinding equipment.

[028] As used herein, the term "scrubbing" refers to any process by which impurities (including, but not necessarily limited to potassium sulphate based salts, dust, water vapor, and H2SO4) are removed from a gaseous product of a chemical reaction.

[029] As used herein, the term "scrubber" refers to any chamber or enclosed volume in which said scrubbing takes place; the use of the term does not exclude the possibility that other processes may occur in the same chamber or volume prior to, contemporaneously with, or subsequent to, said scrubbing. [030] The process of the invention referred to as the HYP AS process can be conducted in three stages. Stage 1 of the low temperature, continuous fine grinding process is the solid-liquid reaction between solid potassium chloride salt and liquid sulphuric acid. Preferably, the liquid sulphuric acid is slowly added to the potassium chloride salt over a specified period of time that can be, for example, between approximately 45 minutes to approximately 60 minutes depending upon the design of the fine grinding equipment, the energy input of the fine grinding equipment, the mass of the solids to be fine ground and the extent of fine grinding. The slow addition of the sulphuric acid assists in preventing the formation of agglomerates or granulates and enabling a free flowing solid material within the fine grinding equipment. The addition of the sulphuric acid can be added continuously over the period of time or be added in portions. The concentration of sulphuric acid can be approximately from 50% to approximately 100% by weight, preferably 98% by weight before being added to the continuous fine grinding process. The Stage 1 process is carried out at a temperature of approximately between 0°C to 100°C,. preferably approximately between 15 to 40°C, to simplify process plant design, according to the chemical reaction scheme [i] below.

Stage 1:

KCI + H ₂ SO ₄ → KHSO ₄ + HC1 [i]

[031 ] Under the conditions of continuous fine grinding in this solid- liquid system the reaction can proceed to 90- 99% completion and can be limited by the fine grinding time and fine grinding energy input. It is expected that for these types of salts the energy input required to fine grind to the desired particle size distribution will be approximately 40 to 60 kWh per tonne depending upon the efficiency of the fine grinding equipment design. For example with commercial fine grinding equipment the fine grinding time can be from approximately 30 to 240 minutes, or from approximately 60 to 120 minutes; or preferably from approximately 30 to 60 minutes. The process of Stage 1 can be influenced by the fine grinding time, grinding energy input and/or the sulphuric acid addition rate. It is preferred that these parameters are selected to enable a substantial portion of the salts in the fine grinding equipment, for example, at least 80% or more of the salts to remain free flowing during Stage 1 of the process.

[032] Stage 1 of the low temperature, continuous fine grinding process does not require external heating in order to proceed. The initial relative mole ratio of the potassium chloride to sulphuric acid used in Stage 1 of the process can be between 1 mol C1 to 0.95 mol H ₂ S0 ₄ up to 1 mol KC1 to 2 moles H ₂ S0 ₄ . Most preferably the mole ratio is 1 mol KC1 to 1 mol H ₂ S0 ₄ . [033] Slow controlled addition of me sulphuric acid to the potassium chloride salt is necessary while fine grinding to keep at least 80% of the solid materials free flowing. If the sulphuric acid addition is too rapid the salts can form an initial sticky mass of salts which can then form larger hard aggregates, granulates or lumps of salts which become difficult to process in the equipment. Gaseous hydrogen chloride HC1 is formed during this acid addition together with powdered potassium hydrogen sulphate. The dry HC1 gas generated can be purified, stored or adsorbed in water to produce aqueous hydrochloric acid. As the reaction proceeds to 100% completion, the levels of residual unreacted potassium chloride and sulphuric acid in the composition decline. The reaction can be terminated before 100% completion provided residual potassium hydrogen sulphate and potassium chloride meet a particular final product specification for these salts as desired.

[034] In Stage 2 of the low temperature continuous fine grinding process the solid potassium hydrogen sulphate from Stage 1 is reacted at a temperature of between 0-100°C with unreacted solid potassium chloride from Stage 1 or additional potassium chloride added during Stage 2 to form hydrogen chloride gas and a solid composition containing potassium sulphate, potassium hydrogen sulphate and potassium chloride. As the reaction proceeds to 100% completion, the levels of residual unreacted potassium hydrogen sulphate and potassium chloride in the solid composition decline. The reaction can be terminated before 100%

completion provided residual potassium hydrogen sulphate and potassium chloride meet a particular final product specification for these salts as desired. [035] The initial relative mole ratios of the potassium hydrogen sulphate and potassium chloride used in Stage 2 of the process can be between 1 mol KCl to 1 mol of KHSO4 up to 1 mole KCl to 2 moles KHSO4. Most preferably the mole ratio is 1 mol KCl to 1 mol KHSO ₄ .

[036] Potassium sulphate can be produced from the reaction between

stoichiometric quantities of potassium chloride and potassium hydrogen sulphate according to the chemical reaction [ii]. Stage 2:

KHSO4 + KCl → K ₂ SO ₄ + HC1 [ii]

[037] Under the conditions of continuous fine grinding in this solid-solid system the reaction is slower than the Stage 1 reaction, but can proceed to 90-99% completion with extended fine grinding time. In a commercial plant depending upon the energy input and design efficiency, the total fine grinding time for the Stage 2 process can typically be from approximately 45 to 360 minutes, or from approximately 90 to 180 minutes; or preferably from approximately 45 to 90 minutes.

[038] Increasing the mole ratio of KHSO4 to KCl will reduce the time to consume all the KCl and leave residual KHSO4 as shown in reaction scheme [iiia] which can optionally be neutralized to produce an acceptable salt blend for fertilizer applications such as the example shown in reaction scheme [iiib].

2KHSO4 + KCl K ₂ S0 ₄ + KHS0 ₄ + HC1 [iiia]

[039] Typically the residual potassium hydrogen sulphate as shown in reaction scheme [iiia] can be neutralized using an agent such as ammonia gas or aqueous ammonium hydroxide in Stage 3 of the process according to reaction scheme [iiib] as shown below. Stage 3:

KHS0 ₄ + NH ₄ OH → KNH4SO ₄ + H ₂ 0 [iiib] [040] The net resulting salts in this example are a mixture of potassium sulphate and potassium ammonium sulphate.

[041] Stage 3 of the process is an optional step of the overall process described herein. During Stage 3 of the process, the residual acidity of the acidic material such as potassium hydrogen sulphate, residual hydrogen chloride and/or residual sulphuric acid resulting rom either Stage 1 or Stage 2 can be neutralized or balanced. In addition, it is also possible to divide the acidic material into two or more portions and neutralize one or more portions and balance one or more portions. The residual acidity of the acidic material can be neutralized by the addition of one or more neutralizing agents such as, but not limited to, ammonia gas, aqueous ammonium hydroxide, magnesium oxide, magnesium carbonate, dolomite (magnesium calcium carbonate), lime or calcium carbonate at a temperature of between approximately 0°C to approximately 100°C.

Alternatively, the residual acidic material can be balanced by the addition of one or more balancing agents such as, but not limited to, magnesium oxide, magnesium carbonate, dolomite (magnesium calcium carbonate), lime or calcium carbonate between approximately 0°C to approximately 100°C. Either neutralization or balancing may be done in the continuous fine grinding equipment, or some other suitable equipment dedicated for this purpose. When the potassium hydrogen sulphate is neutralized, the neutralization step of the process occurs under continuous fine grinding until testing by titration or pH measurements shows that a satisfactory level of neutralization is achieved. The duration of find grinding will depend on the neutralization agent used. When the potassium hydrogen sulphate is mixed or blended with one or more balancing agents, the process may or may not occur under continuous fine grinding. The neutralization reaction between the potassium hydrogen sulphate and the balancing agent(s) does not occur until water is added or the mixture comes into contact with water vapour or an aqueous environment. [042] Stage 3 of the process proceeds according to the following reactions and depending on the neutralizing agent used, different mixed sulphate salts can be produced as shown in reaction schemes [iiib]-[iiih]. If desired, it is also possible to use a mixture of neutralizing agents during Stage 3 such that a mixture of mixed potassium based sulphate salts will form. The additional step of converting the potassium hydrogen sulphates in the fine grinding equipment to potassium based ammonium, magnesium or calcium sulphates by adding a predetermined quantity of at least one suitable neutralizing agent is optional.

KHSO ₄ + NH ₄ OH (aqueous) → K H ₄ SO ₄ + H ₂ O [iiib] KHSO ₄ + H ₃ (gas) → K H ₄ SO ₄ [iiic] 2KHSO4 + Mg(OH) ₂ → K ₂ Mg(S0 ₄ ) ₂ + 2H ₂ O |iiid| 2 HS0 ₄ + MgCQj → K2Mg(S0 ₄ ) ₂ + HiO +CO2 [iiie] 2 HSO ₄ + (CaJVIg) CQj → K ₂ (Ca/Mg)(S0 ₄ ) ₂ + H ₂ O +CO ₂ (rail 2KHSO ₄ + Ca(OH), → K ₂ Ca(S0 ₄ ) ₂ + 2HzO [iiig] 2KHSO4 + CaCOs → K2Ca(S0 ₄ ) ₂ + H ₂ O + X [vah]

[043] Each neutralization equipment could be designed for use with the specific neutralizing agent used; e.g. any particular neutralization chamber can be adapted for use with a gaseous neutralizing agent (e.g. gaseous NH3, etc.), a liquid neutralizing agent (e.g. aqueous NH ₄ OH, etc.), or a solid neutralizing agent (e.g. MgO, MgC0 ₃ , Ca(OH) ₂ , CaC0 ₃ ), according to the needs of the user. Containers and reactors adapted for such substances are well known to those skilled in the art.

[044] Addition of one or more balancing agents can require only simple powder mixing or blending with the potassium salts, as they do not need to react in order to neutralize the acidity of potassium hydrogen sulphate in Stage 3 of the process. Neutralisation will only occur when the balancing agent and potassium salt mixture is exposed to water at a later stage which for example might be when they are applied to wet soil. [045] The finely ground powders of the potassium hydrogen sulphate, potassium sulphate and potassium based ammonium, magnesium or calcium sulphates may be removed from the fine grinding equipment by a pneumatic system with a size classifier or other suitable conveying system.

[046] The fine salt powders may be processed into granules or pellets with addition of minor binding agents and water as necessary. Examples of binding agents could include bentonite clay, urea formaldehyde, xanthan gums, gelatine and/or organic polymers.

[047] In addition, the gaseous HC1 produced by the process can optionally be transferred to a sulphuric acid or aqueous HC1 scrubber to remove any solid salts or other impurities. Alternatively, the gaseous HC1 can be transferred to a water scrubber with the necessary cooling equipment to remove the heat generated by the hydrogen chloride gas dissolving in the water. The aqueous HC1 discharged from the scrubber can be obtained in a concentration of greater than about 33% by weight dissolved HC1.

[048] The invention will now be described further, and by way of example only, with reference to the following non-limiting examples.

[049] It is to be understood that the present invention has been described by way of example only and that modifications and/or alterations thereto, which would be apparent to a person skilled in the art based upon the disclosure herein, are also considered to fall within the scope and spirit of the invention, as defined in the appended claims.

EXAMPLE 1 [050] This example shows Stage 1 of the process which produces potassium hydrogen sulphate KHSO4 and HC1 using a reactant mole ratio of approximately one mole of KC1 to one mole of H2SO4. KCl (s) + H ₂ S0 ₄ (1)→ KHSO4 (s) + HCl (g) [i]

[051] 74.5 grams of potassium chloride KCl (1 mol) was ground in a laboratory fine grinding mill for 5 minutes at 25°C. A total of 96 grams (0.96 moles) of 98% sulphuric acid was slowly fed into the mill over a period of 60 minutes with continuous fine grinding until hydrogen chloride gas ceased to evolve after an additional 30 minutes. Thus, the conversion of potassium chloride and sulphuric acid to potassium hydrogen sulphate and residual potassium chloride occurred within 90 minutes.

[052] The finely ground salts were analyzed by titration with standardized sodium hydroxide solution for total acidity which was then used to calculate acid loss as HCl gas and conversion of KCl to KHSO4. The final salt composition was calculated to be 95%w/w KHSO4 and 5% w/w KCl and a total of 35 grams of HCl was generated.

EXAMPLE 2

[053] This example shows Stage 1 and Stage 2 of the process carried out consecutively without interruption using a reactant mole ratio of one mole of KCl to 0.5 moles ofH ₂ SO ₄ .

[054] 74.5 grams of potassium chloride KCl (1 mol) was ground in a fine grinding mill for 5 minutes at 25°C. A total of 50.0 grams (0.5 mol) of 98% sulphuric acid was slowly fed into the mill over a period of 60 minutes with continuous fine grinding until the evolution of hydrogen chloride slowed down. After a further 30 minutes, 60 minute and 90 minutes of fine grinding, samples of the salt composition in the mill were taken and analyzed for residual acidity by titration with standardized sodium hydroxide solution.

KCl (s) + 0.5 H2SO4 (1) → 0.5 KHSO ₄ (s) + 0.5 HCl (g) + 0.5KC1 (s) Stage 1 O.SKCHsl + O.SKHSO^ fs)→ 0.5K ₇ SO_ (s) + 0.5 HCl (g) Stage 2 [055] Using a 1 mol KCl to 0.5 mol H ₂ S0 ₄ , Stage 1 and Stage 2 of the process combined results in: KCl + 0.5 H ₂ SO ₄ → 0.5K ₂ SO ₄ + HC1

74.55 + 49.04 87.13 + 36.5

[056] The w/w percentage of KCl, KHSO4 and K ₂ S0 ₄ relative to the total mass of KCl + KHSO4 + K ₂ S0 ₄ in the samples taken of the salt composition was calculated based on the residual acidity observed after the specified further fine grinding time intervals as follows. After 30 minutes of further fine grinding time, the salt composition comprised 12.8 %w/w KHS0 ₄ ; 80 %w/w K ₂ S0 ₄ and 7 %w/w KCl. After 60 minutes of further fine grinding time, the salt composition comprised 8.6%w/w KHSO4; 86.4 % w/w K ₂ S0 ₄ and 4.8 %w/w KCl. After 90 minutes of further fine grinding time, the salt composition comprised 6 %w/w

KHSO4, 90 %w/w K ₂ S0 ₄ and 3.5 %w/w KCl.

EXAMPLE 3 [057] This example shows Stage 1 and Stage 2 of the process carried out consecutively without interruption by adding a 50% mole excess of sulphuric acid compared to the amount of sulfuric acid used in Example 2.

[058] 74.5 grams of potassium chloride (1 mol) was ground in the fine grinding mill for 10 minutes at 25°C. A total of 75.1 grams (0.75 mol) of 98% sulphuric acid was slowly fed into the mill over a period of 60 minutes with continuous fine grinding until hydrogen chloride ceased to evolve after an additional 30 minutes. A sample of the salt composition in the mill was taken and analyzed by titration with standard sodium hydroxide solution. Based on the residual acidity of the salt composition, it was determined that the w/w percentage of KCl, KHS0 ₄ and

K ₂ S0 ₄ relative to the total mass of KCl + KHSO4 + K ₂ S0 ₄ was 54 % w/w KHSO4, 44 % w/w K ₂ S0 ₄ , and 2 % w/w KCl. The chemical equations of Stage 1 and Stage 2 of the process described in Example 3 are shown below. KC1 + 0.75 H ₂ SO ₄ -→ 0.75 KHSO ₄ + 0.25KC1 + 0.75 HC1 Stage 1 0.75 KHS(X« + 0.25KC1→ 0.25 K^SC + 0.5 KHSOi + 0.25 HC1 Stage 2 KC1 + 0.75H ₂ SO ₄ →0.25 K ₂ SO + 0.5 KHSO ₄ + HC1 Stage 1 plus Stage 2

EXAMPLE 4

[059] This example shows the neutralization of the potassium hydrogen sulphate from Example 1 using aqueous ammonium hydroxide (28%w/w N¾) as the neutralizing agent.

KHSO ₄ + NH ₄ OH → KNH ₄ SO ₄ + H ₂ 0 [iiib]

[060] 50 grams of the potassium hydrogen sulphate salts from Example 1 was neutralized with the slow addition of 22.3 grams of aqueous NH ₄ OH (28%w/w NH3) at an initial temperature of 25°C with continuous fine grinding.

[061] A 1% solution of the salts had a pH of 6.5. EXAMPLE 5

[062] This example shows the neutralization of the potassium hydrogen sulphate from Example 3 using aqueous ammonium hydroxide (28% NH3) as the neutralizing agent.

KHSO ₄ + NH ₄ OH → KNH ₄ SO ₄ + H ₂ 0 [iiib]

[063] In this experiment, 50 grams of the salt composition from Example 3 containing 54% w/w KHSO4 (27 grams KHS04) were neutralized with 12.0 grams of aqueous NH4OH (28% NH3) at an initial temperature of 25°C with continuous fine grinding. 12.0 grams was equivalent to 3.37 grams of ammonia gas (N¾) for neutralization of the KHSO4. [064] The neutralized dry salts comprised 56 % w/w KNH4SO4, 42 % w/w K ₂ S0 ₄ and 1.8% w/w C1.

[065] A 1% solution of the salts had a pH of 6.4.