Sulfuric Acid For Gardening Omri

Sulphuric Acid

Sulfuric acid is the main ingredient in the electrolyte, which, depending on the concentration, can have a great deal of corrosion on the metals.

From: Simulation of Battery Systems , 2020

Sulfuric Acid

A. Saeid , K. Chojnacka , in Encyclopedia of Toxicology (Third Edition), 2014

Reactivity

Sulfuric acid is very reactive and dissolves most metals, it is a concentrated acid that oxidizes, dehydrates, or sulfonates most organic compounds, often causes charring.

Sulfuric acid reacts violently with alcohol and water to release heat. It reacts with most metals, particularly when diluted with water, to form flammable hydrogen gas, which may create an explosion hazard. Sulfuric acid is not combustible, but it is a strong oxidizer that enhances the combustion of other substances, does not burn itself. During fire, poisonous gases are emitted. Hazardous decomposition products are as follows: sulfur dioxide, sulfur trioxide, and sulfuric acid fumes.

Note: Use great caution in mixing with water due to heat release that causes explosions. Always add the acid to water, never the reverse.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123864543009908

Sulfuric Acid

Heriberto Robles , in Encyclopedia of Toxicology (Second Edition), 2005

Mechanism of Toxicity

Sulfuric acid is a highly reactive chemical. It can react with cells and tissues upon contact. Damage caused by sulfuric acid can range from tissue irritation to chemical burns and necrosis. Signs and symptoms of exposure include tissue damage at point of contact. Tissue injury appears within seconds of exposure and can continue for hours and even days if not properly treated. The tissue damage extent and severity is dependent on the dose received, exposure interval, and strength (molar concentration) of the sulfuric acid solution. Highly concentrated sulfuric acid solutions (usually found in industrial chemicals) are more dangerous than diluted acid solutions (as those found in consumer products).

The mode of action of sulfuric acid is the same in humans and animals. Therefore, acute and chronic effects are expected to be the same for animals and humans.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0123694000009121

Industry Profile—Fertilizers

Paul N. Cheremisinoff P.E., D.E.E. , in Waste Minimization and Cost Reduction for the Process Industries, 1995

Sulphuric Acid

Sulphuric acid is produced from sulphur. Sulphur dioxide is first obtained by the burning of the molten sulphur in presence of air. Sulphur dioxide is then converted to sulphur trioxide in presence of vanadium pentoxide catalyst. The sulphur trioxide thus obtained is absorbed in recycling concentrated sulphuric acid in an absorption tower. The plants installed earlier and the smaller units of sulphuric acid plants use a single absorption process which has conversion efficiency of 96–98%. New large sulphuric acid production plants now–a–days utilize double conversion double absorption (DCDA) process. DCDA process can realize above 99% conversion efficiency. The manufacturing process for sulphuric acid by the single absorption process and DCDA process are shown in Figure 7–9 and Figure 7–10 respectively.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780815513889500099

Recovery of Waste Printed Circuit Boards Through Pyrometallurgy

En Ma , in Electronic Waste Management and Treatment Technology, 2019

3.1.6.2 Salt Roasting

Sulfuric acid roasting and chlorination roasting are typical examples of salt roasting. The aim is to convert as many metallic sulfides or oxides in the material into soluble salts dissolved in water, or dilute acids, under controlled conditions. The main control conditions of sulfuric acid roasting are temperature and air volume. At the same temperature, the decomposition pressure and stability of various sulfates are different; the higher the temperature, the more unstable the sulfate is, and the easier it is to decompose into oxides. The selective sulfuric acid roasting is carried out by controlling the temperature by the difference of sulfate stability. When the air volume can be the maximum value of the SO₃ in the gaseous phase, it is the most suitable volume for sulfuric acid roasting. Sulfuric acid roasting is applied to the treatment of copper concentrate, copper-cobalt concentrate, cobalt-sulfur concentrate and low-grade metal material. The fluidized roasting furnace is used for sulfuric acid roasting in industry.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B978012816190600011X

Sources of air emissions from pulp and paper mills

Nicholas P. Cheremisinoff , Paul E. Rosenfeld , in Handbook of Pollution Prevention and Cleaner Production, 2010

Sulfuric acid

Sulfuric acid (CASRN 7664-93-9), also known as hydrogen sulfate, is a highly corrosive, clear, colorless, odorless, strong mineral acid with the formula H₂SO₄. It is also one of the top 10 chemicals released (by weight) by the paper industry (US EPA, 2009). In modern industry, sulfuric acid is an important commodity chemical, and is used primarily for the production of phosphoric acid. It is also good for removing oxidation from iron and steel, so it is used in large quantities by metal manufacturers.

Sulfuric acid is a very dangerous chemical. It is extremely corrosive and toxic. Exposure can occur from inhalation, ingestion, and through skin contact. Inhalation of H₂SO₄ may cause irritation and/or chemical burns to the respiratory tract, nose, and throat. Inhalation can also be fatal as a result of spasm, inflammation, edema of the larynx and bronchi, chemical pneumonitis, and pulmonary edema. Chronic inhalation is known to have caused kidney and lung damage in addition to nosebleeds, erosion of the teeth, chest pain, and bronchitis.

The effects of ingesting sulfuric acid orally are just as bad as inhalation. Ingestion may cause systematic toxicity with acidosis, which can be fatal. It can also cause severe permanent damage to the digestive and GI tracts. Prolonged or repeated ingestion is not common because the first ingestion is usually the last.

Skin or eye contact with sulfuric acid can be devastating. The burns induced are similar, and often worse, than those caused by hydrochloric acid. What makes sulfuric acid so dangerous is its exothermic reaction with water. When introduced to water or moisture, the solution reacts with the water to create hydronium ions. This reaction releases large amounts of heat to the environment. This reaction is so strong that concentrated sulfuric acid can char paper by itself (see Figure 6.10). Recurring contact with the skin is known to cause dermatitis, and repeated contact with the eyes can cause permanent visual problems.

Another deadly property of sulfuric acid is its carcinogenicity. The International Agency for Research on Cancer (IARC) has classified "strong inorganic acid mists containing sulfuric acid" as a group 1 known human carcinogen. The ACGIH also classified sulfuric acid mists as a category A1 carcinogen. This only applies to mists, and not to liquid sulfuric acid and its solutions (ISU, 2000). Table 6.20 shows toxicology values for sulfuric acid.

Table 6.20. Toxicological characterization data for sulfuric acid

RfC	LD₅₀ (rats)	LC₅₀ (rats)	LOAEL	NOAEL	PEL
0.001 mg/m³	2.14 g/kg	510 mg/m³ (2 h)	380 mg/m³	N/A	1 mg/m³

Source: ISU (2000).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780080964461100061

Industrial Inorganic Chemistry

DR. James G. Speight , in Environmental Inorganic Chemistry for Engineers, 2017

3.3.15 Sulfuric Acid

Sulfuric acid (H₂SO₄) (the historical name oil of vitriol) is an inorganic chemical that is a highly corrosive strong mineral acid that is a pungent-ethereal, colorless to slightly yellow viscous liquid that is soluble in water at all concentrations. Sometimes, the acid may be sold as a dark brown liquid (dye added during production) to alert purchases the hazards of handling this acid.

Sulfuric acid is manufactured in large quantities on a world scale with the production of the chemical often being linked to the stage of development of a country, owing to the large number of transformation processes in which it is used. Sulfuric acid (H₂SO₄) is a basic raw material used in a wide range of industrial processes and manufacturing operations. A high proportion of the manufactured sulfuric acid is used in the production of phosphate fertilizers and other uses include copper leaching, inorganic pigment production, petroleum refining, paper production, and industrial organic chemical production.

Sulfuric acid is manufactured from elemental sulfur in a three-stage process:

$S + O_{2} \to {SO}_{2}$

$2 {SO}_{2} + O_{2} \to 2 {SO}_{3}$

${SO}_{3} + H_{2} O \to H_{2} {SO}_{4}$

Since the reaction of sulfur with dry air is exothermic, the sulfur dioxide must be cooled to remove excess heat and avoid reversal of the reaction.

The combustion of elemental sulfur is the predominant source of sulfur dioxide used to manufacture sulfuric acid. The combustion of hydrogen sulfide from waste gases, the thermal decomposition of spent sulfuric acid or other sulfur-containing materials, and the roasting of pyrites are also used as sources of sulfur dioxide. Sulfuric acid may be manufactured commercially by either the lead chamber process or the contact process with a modern leaning toward the contact process.

In the contact process, the process plants are generally characterized according to the raw materials charged to them: (1) combustion of elemental sulfur, (2) combustion of spent sulfuric acid and hydrogen sulfide, and (3) combustion of metal sulfide ores and smelter gas burning. More specifically, the contact process incorporates three basic operations, each of which corresponds to a distinct chemical reaction. First, the sulfur in the feedstock is oxidized (burned) to sulfur dioxide:

$S + O_{2} \to {SO}_{2}$

The resulting sulfur dioxide is fed to a process unit (often referred to as the converter) where it is catalytically oxidized to sulfur trioxide:

$2 SO + 2 O_{2} \to 2 {SO}_{3}$

Finally, the sulfur trioxide is absorbed in a strong sulfuric acid (98%) solution:

${SO}_{3} + H_{2} O \to H_{2} {SO}_{4}$

In the Frasch process, elemental sulfur is melted, filtered to remove ash, and sprayed under pressure into a combustion chamber where the sulfur is burned in clean air that has been dried by scrubbing with 93%–99% (v/v) sulfuric acid. The gases from the combustion chamber are cool by passing through a waste heat boiler and then enter the catalyst (vanadium pentoxide, V₂O₅) converter. Typically, 95%–98% (v/v) of the sulfur dioxide from the combustion chamber is converted to sulfur trioxide, with an accompanying large evolution of heat. After being cooled, again by generating steam, the converter exit gas enters an absorption tower. The absorption tower is a packed column where acid is sprayed in the top and the sulfur trioxide enters from the bottom. The sulfur trioxide is absorbed in the 98%–99% (v/v) sulfuric acid where the sulfur trioxide combines with the water in the acid and forms more sulfuric acid. If oleum (a solution of uncombined sulfur trioxide dissolved in sulfuric acid) is produced, sulfur trioxide from the converter is first passed to an oleum tower that is fed with 98% (v/v) acid from the absorption system. The gases from the oleum tower are then pumped to the absorption column where the residual sulfur trioxide is removed. The single absorption process uses only one absorber as the name implies, but many plants have installed a dual absorption step.

In the dual absorption step, the sulfur trioxide gas formed in the primary converter stages is sent to an interpass absorber where most of the sulfur trioxide is removed to form sulfuric acid. The remaining unconverted sulfur dioxide is forwarded to the final stages in the converter to remove much of the remaining sulfur dioxide by oxidation to sulfur trioxide, from whence it is sent to the final absorber for removal of the remaining sulfur trioxide.

If oleum (fuming sulfuric acid, simply represented as H₂SO₄·SO₃) is produced (a mixture of excess sulfur trioxide and sulfuric acid), sulfur trioxide from the converter is passed to an oleum tower that is fed with 98% (v/v) acid from the absorbers. The gases from this tower are then pumped to the absorption column where sulfur trioxide is removed. Various concentrations of oleum can be produced. Common ones include 20% oleum (20%, v/v sulfur trioxide in 80%, v/v sulfuric acid, with no water), 40% oleum, and 60% oleum.

Sulfur dioxide is the primary emission from sulfuric acid manufacture and is found primarily in the exit stack gases. Conversion of sulfur dioxide to sulfur trioxide is also incomplete during the process, which gives rise to emissions. Dual absorption is considered the best available control technology (BACT) for meeting NSPS for sulfur dioxide. In addition to stack gases, small amounts of sulfur dioxide are emitted from storage and tank-truck vents during loading, from sulfuric acid concentrators, and from leaking process equipment.

Acid mists may also be emitted from absorber stack gases during sulfuric acid manufacture. The very stable acid mist is formed when sulfur trioxide reacts with water vapor below the dew point of sulfur trioxide. Typical control devices include vertical tube, vertical panel, and horizontal dual pad mist eliminators.

During the production of sulfuric acid, a sludge is produced in the carbon dioxide removal unit used to absorb solvent gas. A hydrocarbon solvent is used in the unit, which breaks down into a hydrocarbon sludge during the process. This sludge is usually combusted in another part of the process. Sulfuric acid manufacture also produces a solid waste containing the heavy metal vanadium, when the convertor catalyst is regenerated or screened. This waste is sent to an off-site vendor for reprocessing. Additional solid wastes from sulfuric acid production may contain both vanadium and arsenic, depending on the raw materials used, and care must be taken to dispose of them properly in landfills.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128498910000035

Pollution and Pollution Prevention

In Handbook of Pollution Prevention and Cleaner Production: Best Practices in the Agrochemical Industry, 2011

2.2.3 Sulfuric Acid Unit

The main features of this unit are:

•: storage facilities
•: sulfur melting and filtration stages.

Sulfuric acid (H₂SO₄) is important in the production of fertilizers (e.g., ammonium sulfate (sulfate of ammonia), (NH₄)₂SO₄, and superphosphate, Ca(H₂PO₄)₂, which is formed when rock phosphate is treated with sulfuric acid). Sulfuric acid is manufactured at the site using the well-known contact process. The process involves the catalytic oxidation of sulfur dioxide, SO₂, to sulfur trioxide, SO₃. The following are the manufacturing steps:

1.: Solid sulfur, S(s), is burned (melted) in air to form sulfur dioxide gas, SO₂ S(s)+O₂(g) → SO₂(g).
2.: The gases are mixed with more air then cleaned by electrostatic precipitation to remove any particulate matter.
3.: The mixture of sulfur dioxide and air is heated to 450°C and subjected to a pressure of 101.3–202.6 kPa (1–2 atmospheres) in the presence of a vanadium catalyst to produce sulfur trioxide, SO₃(g), with a yield of 98%. 2SO₂(g)+O₂(g) → 2SO₃(g).
4.: Any unreacted gases from the above reaction are recycled back into the above reaction.
5.: Sulfur trioxide, SO₃(g) is dissolved in 98% (18M) sulfuric acid, H₂SO₄, to produce disulfuric acid or pyrosulfuric acid, also known as fuming sulfuric acid or oleum, H₂S₂O₇. SO₃(g)+H₂SO₄ → H₂S₂O₇.This is done because when water is added directly to sulfur trioxide to produce sulfuric acid SO₃(g)+H₂O(l) → H₂SO₄(l) the reaction is slow and tends to form a mist in which the particles refuse to coalesce.
6.: Water is added to the disulfuric acid, H₂S₂O₇, to produce sulfuric acid, H₂SO₄ H₂S₂O₇(l)+H₂O(l) → 2H₂SO₄(l).

The oxidation of sulfur dioxide to sulfur trioxide in step (3) above is an exothermic reaction (i.e., energy is released). Hence, a by-product of this process is steam.

Higher temperatures will force the equilibrium position to shift to the left-hand side of the equation favoring the production of sulfur dioxide. Lower temperatures would favor the production of the product sulfur trioxide and result in a higher yield. However, the rate of reaching equilibrium at the lower temperatures is extremely low. A higher temperature means equilibrium is established more rapidly but the yield of sulfur trioxide is lower. A temperature of 450^oC is a compromise whereby a faster reaction rate results in a slightly lower yield. Similarly, at higher pressures, the equilibrium position shifts to the side of the equation in which there are the least numbers of gaseous molecules:

$2 {SO}_{2} (g) + O_{2} (g) \to 2 {SO}_{3}$

On the left-hand side of the reaction there are 3 moles of gaseous reactants, and on the right-hand side there are 2 moles of gaseous products, so higher pressure favors the right-hand side. Higher pressure results in a higher yield of sulfur trioxide. A vanadium catalyst is used in this reaction in order to speed up the rate of the reaction.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9781437778250000029

Roasting of Gold Ore in the Circulating Fluidized-Bed Technology

J. Hammerschmidt , ... A. Charitos , in Gold Ore Processing (Second Edition), 2016

4.3.4 Sulfuric Acid Plant

The sulfuric acid plant can be divided into three main sections: drying and adsorption, SO₂ converter with gas-to-gas heat exchangers and tail gas scrubber. The plant uses the 3 + 1 double-absorption system. The acid plant can operate in four production modes. Modes one and three are for production of 94% sulfuric acid and Modes two and four for 98.5% sulfuric acid production. Any mode of operation can use single, double or partial-double absorption depending upon the incoming SO₂ concentration in the process gas. The final SO₂ conversion is typically greater than 99.8%.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444636584000244

Karst Geomorphology

A.N. Palmer , in Treatise on Geomorphology, 2013

6.20.4.2 Related Cave Features

Sulfuric acid caves contain many small features that contribute little to the cave pattern, but which offer evidence for their origin. Most diagnostic are thick rinds and masses of gypsum that have replaced carbonate bedrock, because they are a direct product of sulfuric acid speleogenesis (Figure 3). Few such rinds are more than 30 cm thick. In most places, they have fallen to the floor to coalesce in thick piles (Figure 4). Gypsum rinds up to a few centimeters thick are also present in some dry epigenic caves where pyrite in the bedrock has oxidized to sulfuric acid. This gypsum tends to be stained brown from iron oxides, whereas most gypsum derived from H₂S oxidation is pure white. Replacement gypsum is easily dissolved by meteoric water that infiltrates from the surface, and also by cave streams, even those that are H₂S sources. Vadose drips commonly core through blocks of gypsum, forming holes with fluted walls. Abrupt terminations of gypsum bodies by dissolution are typical of sulfuric acid caves (Figure 4).

Solution pockets are abundant in nearly all bedrock surfaces of sulfuric acid caves (Figures 4 and 14). Many are produced by the localized action of sulfuric acid, but others by subaerial dissolution where water from infiltration or condensation absorbs H₂S or CO₂. Also, many pockets are the remnants of lobate reaction fronts between gypsum and carbonate rock during sulfuric acid speleogenesis. When the gypsum crust falls off or is dissolved away, pockets are revealed in the bedrock surface. Many of these resemble scallops (asymmetrical solution pockets formed by flowing turbulent water). Many people scrutinize these in unsuccessful attempts to determine former flow directions and velocities. True scallops are rare in sulfuric acid caves, even in active stream beds, perhaps because the intensity and irregularity of sulfuric acid dissolution overwhelm the influence of the moving water. Also, the flow rate in most sulfuric acid caves is too low to form scallops.

Ceiling channels and cupolas (rounded ceiling pockets) are widely considered to be evidence for hypogenic cave origin, where the water once contained local convection cells. Yet many of these features are formed or enlarged by condensation corrosion above the water table, in both active and inactive caves, and by local enlargement along fractures as in other types of solution pocket.

Rills and potholes are formed in carbonate walls and floors where sulfuric acid drips from overlying gypsum (Figure 5) or strands of bacterial filaments (see Section 6.20.3.2). When the overlying features disappear by dissolution or by cessation of sulfuric acid processes, the bare bedrock above the rills and potholes seems to show no relation to the intense dissolution beneath them.

The floors of many rooms and passages in Guadalupe caves are riddled with spongework. This phenomenon is also present in parts of the Frasassi System in Italy. These areas were once floored by thick gypsum, which in many areas has been dissolved away by infiltrating vadose water. Rills line some of the spongework holes. The spongework is probably formed by thin water films rather than discrete drips. Gypsum can also sag into the underlying holes and deliver aggressive water directly to bedrock surfaces, as though by the application of an acid-soaked sponge.

Highly altered and weathered bedrock surfaces are common (Figure 4). One effect is the bleaching of bedrock by sulfuric acid, mainly because of oxidation of organics and diminution of crystal size (micritization), and occasionally dolomitization (Palmer, 2007). Even in supposedly inactive caves, absorption of CO₂ and perhaps H₂S by condensation moisture and infiltration can corrode the bedrock surfaces, especially ceilings and upper walls where condensation is most active. Where bedrock in contact with corrosive air has a large insoluble content, iron and manganese minerals are readily oxidized and produce a multicolored fluffy or granular rind. This process is speeded by the action of various microbes, and their filaments are common in the weathered material. The combination of weathered bedrock and organics constitutes a kind of soil. For that reason, these weathering rinds can be called speleosols (Maltsev et al., 1997; Spilde et al., 2009).

As a result of subaerial weathering, the floors and other upward-facing surfaces of sulfuric acid caves are commonly covered with a powder of weathered bedrock. The powder can accumulate to thicknesses of several centimeters, or much more where it is concentrated beneath chutes or wall channels. Where moisture is abundant, this material instead consists of a paste that oozes by gravity, coats large surfaces, and may eventually recrystallize as a hard white crust (Palmer, 2007).

Distinctive minerals are produced by H₂S oxidation and the sulfuric acid attack of bedrock (Polyak and Provencio, 2001). Elemental sulfur is present in a few places where oxidation of H₂S has been incomplete. It is most stable at low pH, so it is most common in or on gypsum or other noncarbonate surfaces. Sulfuric acid can alter clays to a variety of minerals such as alunite (KAl₃(SO₄)₂(OH)₆) and hydrated halloysite (Al₂Si₂O₅(OH)₄·2H₂O). To have a strong enough acid to produce these, the reaction must be subaerial and in water films on clay rather than in carbonate-rich water. For example, the pH must be less than about 4 to produce alunite in a typical cave environment (Palmer, 2007). Therefore, these minerals are evidence for vadose speleogenesis. The alteration process also releases silicic acid (H₄SiO₄), which can precipitate as opal or quartz, either as linings on bedrock or mineral surfaces, or as pore fillings. Alunite can be used to date the latest phase of cave enlargement by sulfuric acid (see the following section).

Sulfuric acid caves are noted for the variety of their speleothems. These include the types common in most caves, but some are specific to sulfuric acid caves. The great amount of replacement gypsum in many of these caves makes it possible for this mineral to be dissolved from upper levels and reprecipitated lower down by evaporation as crusts and chandelier-like crystal arrays. Many speleothems are hosted by microbial filaments, which are encased in calcite to form finger-like projections or web-shaped lattices after speleogenesis ceases (Queen and Melim, 2006). Subaqueous helictites are formed where tendrils of calcite-saturated water seep into pools with high concentrations of dissolved gypsum. The common-ion effect forces the calcite to precipitate as worm-shaped features with central canals. They are very rare and have so far been identified only in a few sulfuric acid caves (Davis et al., 1990). Rusticles are iron oxide deposits formed by dissolution of iron oxides in strong acids and reprecipitation when they encounter carbonate-rich water. Because the pH rises, the iron precipitates as hydroxides and oxides. These commonly take the shape of irregular stalactites, which may later become coated with calcite (Davis et al., 1990).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123747396001330

Water and Membrane Treatment

Rajindar Singh , in Membrane Technology and Engineering for Water Purification (Second Edition), 2015

In-line pH adjustment

Membrane scaling is linked to system recovery and cross-flow velocity; generally speaking, for recovery up to 70%, and with or no iron present, acidification may be the only chemical pre-treatment necessary to prevent scaling by calcium carbonate. When water recovery is 75–80%, additional processes such as scale inhibitors and/or IX softening instead of acidification is required. The solubility of calcium carbonate depends on the pH of feed water. The equilibrium can be shifted to the right to convert calcium carbonate to soluble calcium bicarbonate [Ca(HCO₃)₂ ] by lowering the pH to 6.0 with sulphuric acid or hydrochloric acid as:

(2.33) $CaC O_{3} + H \leftrightarrow C a^{2 +} + HC O_{3}$

Acid reacts with bicarbonate alkalinity to produce carbon dioxide. RO permeate is often high in anions and always acidic (pH < 7.0) due to the presence of dissolved carbon dioxide (carbonic acid). Carbon dioxide concentration can be several hundred ppm when using acidified feed [37]. Dissolved carbon dioxide is removed by tower decarbonation or by membrane degasification to reduce the loading on anion resins when EDI or mixed-bed IX is used for producing DI water. Membrane degasification is preferred in high-purity water systems to prevent contamination. Alternately, IX softening is used to remove calcium ions followed by raising the pH of the softened water to 8.3–8.5 by adding caustic soda. Raising the pH with sodium hydroxide converts the carbon dioxide to sodium bicarbonate, which is easily rejected by RO membrane.

Acid addition is determined by the LSI or SDSI of RO reject water. To control calcium carbonate scaling by acid addition alone, the LSI or SDSI in the concentrate stream must be negative as indicated in Table 2.6. When an anti-scalant (A/S) is used, the LSI can be 1.0. LSI is applicable when the TDS is less than 10,000 mg/l, whereas SDI is applied when the TDS is greater than 10,000 mg/l.

Sulphuric acid is commonly used but hydrochloric acid is preferred when the scaling potential is high due to CaSO₄, SrSO₄, and BaSO₄. Calcium sulphate is more soluble than BaSO₄ and SrSO₄. However, since calcium ion is present in natural water sources more abundantly than barium and strontium ions, CaSO₄ is a greater problem. Nevertheless, BaSO₄ and SrSO₄ scale is difficult to re-dissolve once precipitated. Hence, overdosing of sulphuric acid must be avoided. Acidification, however, has several limitations:

•: Low pH increases fouling by natural organic matter (NOM) such as humic acids.
•: Low pH lowers permeate quality due to higher TDS of feed water and increase in silica and carbonic acid.
•: Permeate TDS increases when using hydrochloric acid because added chloride has a lower rejection than sulphate. Hence, acid treatment is usually used for carbonates and phosphates scale prevention.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444633620000021