Acid solutions, processes for preparing same, and uses thereof

Abstract

A process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHS), said process comprising the steps: adding concentrated sulfuric acid to an aqueous sodium chloride solution to produce an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSOs), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSOs concentration of about 15-35% wt / wt.

Description

[0001] Acid Solutions, Processes for Preparing same, and Uses thereof

[0002] Field

[0003] The present invention relates to acid solutions and manufacturing processes for preparing said acid solutions. The acid solutions of the present invention are intended to be used in lowering the pH of pools and spas both in a commercial and domestic setting.

[0004] Background

[0005] In recreational aquatic facilities such as pool and spas, pH is one of the most critical element of water quality. Many commercial pool operators use high pH forms of chlorine as their primary disinfectant source, such as calcium hypochlorite and sodium hypochlorite. These disinfectants are both typically characterized as having a pH up to 11 and 13, which when added to pool water will cause an increase in alkalinity. As the optimum pool water pH is approximately in the 7.2 to 7.8 range, one often requires the addition of an acid source (H+) to bring the pH down to within the optimal range. The most common of these acid sources is sodium bisulfate (NaHSCk), hydrochloric acid (HCI), sulphuric acid (H2SO4) and carbon dioxide (CO2).

[0006] The disadvantages of currently used pool acids are as follows:

[0007] Sulphuric Acid

[0008] For most uses sulphuric acid needs to be sold as diluted product to reduce corrosivity and minimize chemical burn hazards. However, diluting concentrated sulphuric acid is difficult due to the high exotherm and hazards involved, including handling. Furthermore, using sulphuric acid eventually builds a high sulphate content in pool / spa water which destroys concrete and tile grout. In addition, excessive sulphates can contribute to scaling (CaSCk). Yet it is often difficult to achieve the desired pH (due to the challenges associated with strong acid / base neutralizations). Concentrated sulphuric acid is typically at about 98% concentration strength and is unsuitable for domestic use due to its strong fuming which is a hazardous respiratory irritant. In an attempt to reduce the fuming, sulphuric acid is often diluted to about 35%~38% and sold as so called "non-fuming" or "no fume" pool acid for pH control. However amounts of acidic aerosol are detectable and of course the other problems associated with using H2SO4 remain. Specialist safety equipment and clothing is recommended when handling even diluted (10-90%) sulphuric acid which is also classified as hazardous. It is a highly corrosive substance which is deemed destructive to eyes, lungs, and skin. Hydrochloric Acid

[0009] Prior to use HCI needs to be diluted to avoid excessive fuming. The fumes are very corrosive and have caused problems in enclosed public pools. This acid also presents a chemical burn risk, although a lesser one compared with sulphuric acid. With that said there is no contribution to build-up of sulphates and HCI adds chlorides for electrolysis to chlorine so is more desirable on this basis.

[0010] Sodium Bisulohate

[0011] NaHSCk which is often presented as a solid needs to be dissolved before adding to a pool or spa. Thus one needs to weigh the product to determine the quantity needed for each specific dose. Like sulfuric acid, NaHSCk adds to the pool sulphate load . It also possesses a low solubility limit (approx. 20% soluble) and so is less potent in solution. With that said, NaHSCk is a weak acid with minimal potential for causing burns and is relatively safe to handle with no corrosive vapors. With the use of NaHSCk it is easier to obtain the desired pH (weak acid / strong and weak base neutralization) than either HCI or H2SO4.

[0012] Carbon dioxide

[0013] When dissolved in water, CO2 converts to carbonic acid which is a mild acid that is effective in reducing and stabilizing pH. However when too much carbon dioxide is added to the pool water, the low pH level is harmful to the pool plaster and can cause etching. Too high of a pH level can cause scale buildup on the pool's surface. CO2 can also leak from dosing systems to quickly present a colourless, odourless asphyxiation risk, and is also capital intensive to enable handling and monitoring of liquefied high pressure gas. The ultimate fate of all CO2 dosed is evolution to the atmosphere, and is such also environmentally unfriendly.

[0014] The present invention seeks to address some of the shortcomings of abovementioned methods for adjusting the pH of pools and spas in both domestic and commercial settings.

[0015] Summary

[0016] The present invention is based on a unique manufacturing method which prepares a no- fume aqueous acid solution based on the following reaction :

[0017] H2SO4 + NaCI = NaHSCk + HCI

[0018] The process involves adding 98% sulphuric acid to a prepared salt solution. There is a mild exotherm from the dilution of the sulphuric acid but in certain embodiments the temperature is kept below 50 °C.

[0019] The inventors prepare the acid solution by conducting the above reaction in water.

[0020] The reaction involves very cheap raw materials, both of which are readily available.

[0021] It was thought that the HCI produced may be emitted from solution, but at specific concentrations the present inventors have found that the HCI remains in solution (not as a suspension or slurry) and cannot be detected (i.e., negligible smell) and as such is a genuine no-fume composition.

[0022] By adjusting the concentration of the reactants the inventors have developed processes to prepare an aqueous composition in the form of a solution that has the following properties / benefits:

[0023] 1 Has the strength equivalent to about 3-25% wt / wt HCI;

[0024] 2 Has zero smell or fume (and therefore more pleasant and safer to handle);

[0025] 3 Has less potential for chemical burns than either sulphuric or hydrochloric acid (and therefore has an improved safety profile);

[0026] 4 Zero corrosive vapours;

[0027] 5 Cheaper to manufacture than hydrochloric acid perse;

[0028] 6 Easy to obtain desired pH;

[0029] 7 Involves no need for dissolving solid acid into water;

[0030] 8 Cheaper to manufacture than hydrochloric acid perse;

[0031] 9 Enables an atmospheric temperature and pressure pH reduction dosing system with no associated asphyxiation risk, and;

[0032] 10 Easy to obtain desired pH.

[0033] The uses (and advantages therefore) of the presently described no-fume aqueous acid solution as disclosed herein are as follows:

[0034] 1 pH adjustment for Pools 8i Spas.

[0035] 2 Acid cleaning of bricks, brickwork, mortar and concrete.

[0036] 3 Pickling acid for metals, such as steel. 4 Cleaning agent for metals such as soldering preparation.

[0037] 5 Cleaning agent for Porcelain.

[0038] 6 Photographic industries.

[0039] 7 Textile industries.

[0040] 8 Rubber Industry.

[0041] 9 pH regulation in water and waste streams.

[0042] 10 Oil well Acidizing.

[0043] In one aspect the invention provides a process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSO4), said process comprising the following steps:

[0044] (i) adding concentrated sulfuric acid to an aqueous sodium chloride solution to produce an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized by an HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

[0045] In another aspect the invention provides a process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said process comprising the following steps:

[0046] (i) providing an aqueous sodium chloride solution which is characterized with a concentration of about 150g to 250g per 1 L of water;

[0047] (ii) providing about 200-500g of concentrated sulfuric acid (about 98%); and

[0048] (iii) adding the concentrated sulfuric acid to the aqueous sodium chloride solution at room temperature and constant stirring, to produce an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized by an HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt. In another aspect the invention provides a process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said process comprising the following steps:

[0049] (i) providing an aqueous sodium chloride solution which is characterized with a concentration of about 3-4 M;

[0050] (ii) providing about 3-4M concentrated sulfuric acid (98%); and

[0051] (iii) adding the concentrated sulfuric acid to the aqueous sodium chloride solution at room temperature and constant stirring, to produce an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

[0052] In a further alternate aspect the invention also provides a process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said process comprising the following steps:

[0053] (i) blending NaHSCk with aqueous HCI to provide an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-40% wt / wt and a NaHSCk concentration of about 5- 25% wt / wt.

[0054] In certain embodiments the process of the present invention may be conducted with specialized chemical equipment and experience. For instance, the reaction vessel and the stirrer is plastic or rubber lined to prevent corrosion. In such embodiments the reaction temperature is kept below 50 °C.

[0055] In other aspect the invention provides an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt. In other aspect the invention provides an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-40% wt / wt and a NaHSCk concentration of about 5-25% wt / wt.

[0056] In certain other embodiments and with reference to all aspects the aqueous acid solution is characterized with a density of between about 1.2 - 1.6 kg / L, such as about 1.3 - 1.5 kg / L.

[0057] Accordingly, in certain other aspects the invention provides an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt, and has a density of between about 1.2 - 1.6 kg / L.

[0058] Accordingly, in certain other aspects the invention provides an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-40% wt / wt and a NaHSCk concentration of about 5-25% wt / wt, and has a density of between about 1.2 - 1.6 kg / L.

[0059] In certain other aspects the invention provides a method of adjusting the pH of a pool or spa water, said method comprising the step of adding an effective amount of an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

[0060] In certain other aspects the invention provides a method of adjusting the pH of a pool or spa water, said method comprising the step of adding an effective amount of an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt, and has a density of between about 1.2 - 1.6 kg / L, such as about 1.3 - 1.5 kg / L.

[0061] In another aspect the invention provides an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said aqueous acid solution prepared by the process as defined in any one of the above aspects. Detailed description

[0062] The present invention only uses the first reaction {NaCI + H2SO4 = HCI + NaHSCk} from the known Mannheim process (detailed below) i.e. :-

[0063] NaCI + H2SO4 = HCI + NaHSCk Reaction 1 (exothermic)

[0064] NaHSCk + NaCI = Na2SC>4 + HCI Reaction 2 (endothermic - typically conducted at 600-700°C)

[0065] In the traditional Mannheim process ("furnace process") the above reactions (especially Reaction 2) require considerable heat for the process to proceed and the reaction is conducted in the dry state, such the dry NaCI (salt) which is sprayed with concentrated sulfuric acid.

[0066] The inventors reviewed the thermodynamics of Reaction 1 to see if the reaction could proceed in an aqueous solution. They identified that if the Gibbs free energy for the reaction is negative, the reaction will proceed.

[0067] The Gibbs Free Energy values are listed below:

[0068] AG° rxn = 2 AG° prod - 2 AG° react

[0069] AG° rxn = -50 kJ / mole (Reaction 1 should proceed)

[0070] It will be appreciated that the present invention provides an aqueous "solution". The skilled person would understand that all components (HCI and NaHSCk) are solubilized within the aqueous phase. This would obviously distinguish the product from corresponding suspensions or slurries. As such the solutions of the present invention are amendable to be pumped or cannulated by automatic dispensing units / machines.

[0071] The invention provides an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCkconcentration of about 15-35% wt / wt,

[0072] In certain embodiments the acid solution is characterized with a HCI concentration of from about 3-25% wt / wt, such as about 4, 5, 6, 8, 10, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or about 25% wt / wt, or any range between any two of the above figures, such as about 5-25% wt / wt, about 10-25% wt / wt or about 14-25% wt / wt.

[0073] In certain embodiments the acid solution is characterized with a NaHSCk concentration of from about 15-35% wt / wt, such as about 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or about 35% wt / wt, or any range between any two of the above figures.

[0074] In all aspects the acid solution is characterized with a density of between about 1.2 - 1.6 kg / L, such as about 1.22, 1.24, 1.26, 1.28, 1.30, 1.32, 1.34, 1.36, 1.38, 1.40, 1.42, 1.44, 1.46, 1.48, 1.50, 1.52, 1.54, 1.56, 1.58, 1.60 kg / L, or any range between any two of the above figures.

[0075] Without wishing to be bound by any particular theory it is postulated that the greater the density the stronger the acid mixture and therefore the higher the concentration of HCI. One would expect that the higher the HCI concentration, the greater potential for HCI fuming yet this is not observed with the current aqueous acid solution of the invention. It is hypothesized that the amount of sodium bisulfate in the solution is able to "stabilize" the HCI in solution and therefore aids in the "no fuming" advantage demonstrated by the aqueous acid solutions of the present invention. In alternative reported previous processes the production and isolation of Hydrochloric Acid and Sodium Bisulphate occurs as separate species, which is achieved, for instance, in the traditional Mannheim process.

[0076] Some previous reported processes describe a process whereby the exotherm from the aqueous dilution of concentrated sulphuric acid is used as a source of heat for completing the two reactions that proceed to make HCI, NaHSCk or NazSCk as separate species.

[0077] In the traditional Mannheim process, all the heat required for the process was supplied from external combustion, no use was made of the potential energy (exotherm by dilution in water) contained by the 98% sulphuric acid.

[0078] The operating temperatures of these previous reported processes are as follows:-

[0079] NaCI + H2SO4 = HCI + NaHSCk Mannheim Reaction 1, 80-120 deg C

[0080] NaHSCk + NaCI = NazSCk + HCI Mannheim Reaction 2, 105-140 deg C

[0081] In contrast and according to the present process, the inventors do not wish to produce separate species of HCI, NaHSCk or NazSCk.

[0082] The presently described process instead produces an aqueous mixture of HCI and NaHSCk without producing any substantial amounts of NazSCk. That is, for instance, the present process does not produce NazSCk in quantities above lOppm.

[0083] Thus present invention provides an acid solution, which one would understand is different from producing a slurry (or suspension) where there are portions of insolubilized salts.

[0084] In the present process, the maximum temperature reached in the aqueous mixture is about 50 deg C. The present process purposely does not to exceed 50 deg C because the preferred reaction equipment is plastic or rubber lined, and excessive temperatures may damage such equipment. Accordingly, and as a further advantage at maximum reaction temperature of 50 deg C, all of the hydrogen chloride remains in solution and is not distilled from solution to produce pure hydrochloric acid as described in many of the previously reported processes.

[0085] In some embodiments the aqueous sodium chloride solution is characterized with a concentration of about 150g to 250g per 1 L of water such as 155g, 160g, 165g, 170g, 175g, 180g, 185g, 190g, 200g, 205g, 210g, 215g, 220g, 225g, 230g, 235g, 240g, and 245g per 1 L of water, or any range between any two of the above figures. In other embodiments the amount of concentrated sulphuric acid (typicallyabout 98%) added is about 200, 250, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, and about 500 g, or any range between any two of the above figures.

[0086] In some aspects aqueous sodium chloride solution is characterized with a concentration of about 3-4 M, such as about 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, or about 3.9, or any range between any two of the above figures.

[0087] In some aspects the 3-4M concentrated sulfuric acid (98%) is added to aqueous sodium chloride solution at about 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, or about 3.9, or any range between any two of the above figures.

[0088] In certain embodiments sodium salt(M):sulphuric acid (M) ratio is about 1: 1 based on 98% concentrated sulphuric acid.

[0089] In certain embodiments sodium salt(M):sulphuric acid (M) ratio is about 1.2: 1 based on 98% concentrated sulphuric acid.

[0090] In certain embodiments sodium salt(M):sulphuric acid (M) ratio is about 1: 1.2 based on 98% concentrated sulphuric acid.

[0091] In cetian manufacturing method involves adding the concentrated sulfuric acid to the aqueous sodium chloride solution at room temperature and constant stirring, to produce the aqueous acid solution of the present invention.

[0092] In certain embodiments room temperature is between 10-30 °C. That is, the reaction is carried out without external cooling means, such as a water jacket or in ice.

[0093] In certain embodiments stirring is conducted via mechanical means.

[0094] In other embodiments the rate of addition of the concentrated sulphuric acid is such that the reaction exotherm during the reaction conditions is maintained below 50 °C. In certain embodiments the aqueous acid solution of the present invention is especially suited for use and storage in enclosed facilities, for instance, automatic-dosing setups in pool auxiliary / pump rooms.

[0095] In certain other aspects the invention provides a method of adjusting the pH of a pool or spa water to a pH of about 7.2 to 7.8, said method comprising the steps of;

[0096] (i) measuring the water pH to ascertain that the pH is greater than about 7.8; and

[0097] (ii) adding an effective amount of an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk) to bring the pH within about 7.2 to 7.8, wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCkconcentration of about 15-35% wt / wt.

[0098] Hydrogen chloride emitted from hydrochloric acid solutions is not absorbed through the skin. Yet direct contact with aqueous solutions of hydrogen chloride (such as HCI) or with concentrated vapor can cause severe chemical burns. Inhalation is an important route of exposure to hydrogen chloride. Its odor and highly irritating properties generally provide adequate warning for acute, high-level exposures. However, only 50% of exposed persons can perceive hydrogen chloride's odour at the occupational health and safety permissible exposure limit (of about 5 ppm), and odor may not provide adequate warning in the workplace. Hydrogen chloride vapor is heavier than air (gas density. 1.3 (air = 1)) and may cause asphyxiation in enclosed, poorly ventilated, or low-lying areas such as pool storage facilities. Children are at a higher risk than adults. That is, children exposed to the same levels of hydrogen chloride as adults may receive a larger dose because they have greater lung surface area to body weight ratios and increased minute volumes to weight ratios. In addition, because of their short stature and that HCI vapor tends to settle in low-lying areas, children may be exposed to higher levels than adults.

[0099] The permissible exposure limit is about less than 5ppm and exposure at about 50ppm is considered to be immediately dangerous to a person's health and may also lead to death. According to the American Industrial Hygiene Association (AIHA) (emergency response planning guideline) the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour, without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action, is about 20 ppm.

[0100] A typical ion chromatography based instrumental detection limit for Cl is 0.2 pg / ml. So assuming a 50 ml liquid sample (at room temperature) then the analytical detection limit would be about 0.05 ppm for HCI and CI2, respectively.

[0101] It is considered that the present invention minimizes HCI vapor ("fume") to below 4ppm such as below 3ppm, below 2ppm, below Ippm or below 0.5ppm.

[0102] The uses (advantages therefore) of the presently described no-fume aqueous acid solution as disclosed herein are as follows:

[0103] 1 pH adjustment for Pools & Spas.

[0104] 2 Acid cleaning of bricks, brickwork, mortar and concrete.

[0105] 3 Pickling acid for metals, such as steel.

[0106] 4 Cleaning agent for metals such as soldering preparation.

[0107] 5 Cleaning agent for Porcelain.

[0108] 6 Photographic industries.

[0109] 7 Textile industries.

[0110] 8 Rubber Industry.

[0111] 9 pH regulation in water and waste streams.

[0112] 10 Oil well Acidizing.

[0113] 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. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0114] Certain embodiments of the invention will now be described with reference to the following examples which are intended for the purpose of illustration only and are not intended to limit the scope of the generality hereinbefore described.

[0115] Examples

[0116] Manufacture Procedure

[0117] NaCI + H2SO4 = HCI + NaHSCk

[0118] 58.4 + 98 = 36.5 + 120.1 Molecular weights.

[0119] 16% HCI contains 173gm / l of HCI.

[0120] The amount of salt required = (58.4 * 173 / 36.5) = 276.8 gm

[0121] The amount of acid required = (98* 173 / 36.5) = 464.5 gm

[0122] The reaction is performed in about 1 litre of water.

[0123] The solution exothermed (heated) to about 50 deg C.

[0124] The reaction mix turned yellowish, indicating the formation of HCI. No HCI smell was detected. The resultant mixture was titrated with IM NaOH using a phenolphthalein indicator and found to be equivalent to 18.48% HCI.

[0125] The neutralization reactions are:

[0126] HCI + NaOH = NaCI + H2O

[0127] NaHSO4+ NaOH = Na2SO4+ H2O

[0128] Without doing a potentiometric titration it is not possible to determine the quantity of each of the acidic species that were formed. The fact that the Gibbs Free Energy for the reaction is so negative and the change of colour are sufficient evidence that the process is valid.

[0129] The experiment was repeated several times and was found to be reproduceable.

[0130] The density of the solution was found to be 1.247 kg / L. Alternative procedure

[0131] The alternative method of manufacture of zero fume aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), including blending Sodium Bisulphate with and into Hydrochloric Acid.

[0132] Prepare a solution of the following composition:-

[0133] 1 Hydrochloric Acid 7.45 % w / w Pure Hydrogen Chloride

[0134] (Need to calculate the Hydrogen Chloride content in the aqueous HCI used)

[0135] 2 Sodium Bisulphate 24.5% w / w Pure material

[0136] 3 Water 68.05% w / w.

[0137] A small exotherm will be observed during the dissolution of the bisulphate in the aqueous HCI.

Claims

The claims defining the invention are as follows:

1. A process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said process comprising the following steps:(i) adding concentrated sulfuric acid to an aqueous sodium chloride solution to produce an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

2. A process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said process comprising the following steps:(i) providing an aqueous sodium chloride solution which is characterized with a concentration of about 150g to 250g per 1 L of water;(ii) providing about 200-500g of concentrated sulfuric acid (98%); and(iii) adding concentrated sulfuric acid to the aqueous sodium chloride solution at room temperature and constant stirring, to produce an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

3. A process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said process comprising the following steps:(i) providing an aqueous sodium chloride solution which is characterized with a concentration of about 3-4 M;(ii) providing about 3-4M concentrated sulfuric acid (98%); and(iii) adding sulfuric acid to the aqueous sodium chloride solution concentrated at room temperature and constant stirring, to produce an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk),wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

4. A process for preparing an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said process comprising the following steps:(i) blending NaHSCk in aqueous HCI to provide an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-40% wt / wt and a NaHSCk concentration of about 5-25% wt / wt.

5. A process for preparing an aqueous acid solution according to anyone of claims 1 to 4 wherein the acid solution is characterized with HCI vapor ("fume") to below 4ppm.

6. A process for preparing an aqueous acid solution according to claim 5 wherein the acid solution is characterized with HCI vapor ("fume") to below Ippm or below 0.5ppm.

7. A process for preparing an aqueous acid solution according to anyone of claims 1 to 6 wherein the process is carried out in reaction equipment which is plastic or rubber lined.

8. A process for preparing an aqueous acid solution according to anyone of claims 1 to 7 wherein the process is carried out at a temperature below 50°C.

9. A process for preparing an aqueous acid solution according to anyone of claims 1 to 8 wherein produces an aqueous mixture of HCI and NaHSCk without producing any substantial amounts of NazSCk.

10. A process for preparing an aqueous acid solution according to claim 9 which produces an aqueous mixture of HCI and NaHSCk without producing any NazSCk.

11. An aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

12. An aqueous acid solution according to claim 11 wherein the aqueous acid solution is characterized with a density of between about 1.2 - 1.6 kg / L.

13. A method of adjusting the pH of pool or spa water, said method comprising the step of adding an effective amount of an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15- 35% wt / wt.

14. A method of adjusting the pH of a pool or spa water, said method comprising the step of adding an effective amount of an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15- 35% wt / wt, and has a density of between about 1.2 - 1.6 kg / L.

15. An aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), said aqueous acid solution prepared by the process as defined in any one of claims 1 to 4.

16. An aqueous acid solution according to claim 11 or 12, which is characterized with HCI vapor ("fume") below 4ppm at room temperature.

17. An aqueous acid solution according to claim 9, which is characterized with HCI vapor ("fume") below Ippm at room temperature.

18. A method of adjusting the pH of a pool or spa water to a pH of about 7.2 to 7.8, said method comprising the steps of;(i) measuring the water pH to ascertain that the pH is greater than about 7.8; and(ii) adding an effective amount of an aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk) to bring the pH within about 7.2 to 7.8, wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt.

19. A method according to claim 18, wherein step (ii) is conducted by an automatic-dosing machine setup.

20. An aqueous acid solution comprising hydrochloric acid (HCI) and sodium bisulfate (NaHSCk), wherein the aqueous acid solution is characterized with a HCI concentration of from about 3-25% wt / wt and a NaHSCk concentration of about 15-35% wt / wt, when used for pH adjustment for pools & spas, acid cleaning of bricks, brickwork, mortar and concrete, pickling of metals, such as steel, as cleaning agent for metals such as soldering preparation, cleaning of porcelain, in applications for the photographic industries, in applications for the textile industries, in applications for the rubber industry, pH regulation in potable water and waste water streams, or in acidizing oil well.

21. An aqueous acid solution according to claim 20 wherein the aqueous acid solution is characterized with a density of between about 1.2 - 1.6 kg / L.

22. An aqueous acid solution according to claim 20 or 21 wherein the aqueous acid solution is characterized without NazSCk.

23. An aqueous acid solution according to anyone of claims 20 to 22 which is not a slurry.

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