sulfate
Enable an agent to recognise inorganic sulfate, assess its chemical form and amount in a material, and determine which measurements or interventions are justified.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an agent to recognise inorganic sulfate, assess its chemical form and amount in a material, and determine which measurements or interventions are justified.
Sulfate is the tetrahedral oxoanion SO₄²⁻ of sulfur in oxidation state +6, and by extension the salts, minerals and organic esters that contain that anion.
It can be Select a sulfate-specific identification or quantification method appropriate to the sample matrix.; Convert explicitly stated sulfate and sulfur reporting bases and reconcile comparable measurements.; Assess possible sulfate release or precipitation using identified phases and documented conditions.; Evaluate separation or removal options against sulfate form, counterions and the intended destination of removed material.; Track sulfate production, consumption and phase transfer through a sulfur balance.; Refer handling decisions to the actual sulfate-bearing substance or mixture and its intended use..
Distinguishing features
Require evidence for SO4^2−: sulfate has four oxygen atoms per sulfur and a net charge of −2; sulfite is SO3^2−.
Distinguish sulfate from hydrogen sulfate, HSO4−, using the stated species and relevant solution conditions; a reported total sulfate value may combine contributions from different forms.
Distinguish inorganic sulfate from an organic sulfate ester by whether an organic group is covalently attached through oxygen.
Treat a result for elemental sulfur or total sulfur as insufficient to identify sulfate without species-specific evidence.
Distinguish a sulfate constituent from its host salt: sodium sulfate and calcium sulfate contain sulfate but do not thereby share solubility or handling properties.
Scope
+ Identification of the sulfate anion and discrimination from other sulfur species
+ Dissolved sulfate, solid-associated sulfate and their relationship within a sample
+ Counterions, sulfate-bearing phases and hydration where they affect sulfate behaviour
+ Sulfate quantities with explicit reporting basis, sample fraction and measurement conditions
+ Processes that release, immobilise, remove, produce or consume sulfate
- Complete identities and properties of individual sulfate salts or minerals
- Whole-water, soil or industrial-stream composition and quality
- Sulfuric acid manufacture and bulk acid handling
- Organic sulfate esters and sulfate-containing surfactants as complete compounds
- Sulfite, sulfide, thiosulfate and other sulfur species except as distinctions or transformation partners
- Organism physiology, clinical interpretation and regulatory compliance decisions
Characteristics
- Identity evidence
- Declared composition; species-selective measurement; phase identification; inferred; unresolved Separates demonstrated sulfate identity from labels or indirect evidence.
- Chemical form
- Free dissolved sulfate; dissolved ion-associated sulfate; solid-phase sulfate; surface-associated sulfate; unresolved mixture Controls what a measurement represents and which interventions could affect the sulfate.
- Host material and counterions
- Links to sample, solution, identified sulfate-bearing phases and relevant cations Sulfate behaviour depends on its surrounding material and associated ions.
- Sulfate quantity
- mol, mol/L, mg/L as SO4, mg/kg as SO4 or explicitly converted sulfur basis Supports comparison and mass balance without confusing sulfate mass with sulfur mass.
- Measured fraction
- Unfiltered sample; operationally dissolved; extractable; identified solid phase; other explicitly defined fraction Different preparation procedures can produce valid results for different sulfate pools.
- Solution conditions
- pH; temperature in °C or K; ionic strength in mol/kg or mol/L with basis stated Provides context for protonation, ion association and mineral equilibria.
- Sulfate-bearing phase hydration
- Identified hydrate; anhydrous phase; mixed phases; unknown; not applicable Water of crystallisation changes formula-based sulfate content and can affect phase behaviour.
- Phase saturation assessment
- Undersaturated; near saturation; supersaturated; undetermined, each relative to a named phase and calculation Supports assessment of possible dissolution or precipitation without assuming that equilibrium has been reached.
- Transformation evidence
- No assessment; stable within observation limits; redistribution between phases; net sulfate production; net sulfate consumption Distinguishes changes in sulfate identity from movement between sulfate pools.
Also called
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.sulfate
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Sulfate identity Establish whether the recorded constituent is inorganic sulfate and how that identity is supported.
A sulfur measurement or a sulfate-like name does not by itself establish the identity this model owns.
Anion recognition
Identify the SO4^2− constituent and distinguish neighbouring sulfur species.
Identity support
Record the chemical claim and the evidence that can distinguish sulfate from other sulfur-containing constituents.
- Does the recorded identity denote inorganic SO4^2−, rather than total sulfur, sulfite or another sulfur species? definition
- Which composition record or analytical observation supports sulfate identity, and what alternatives can it exclude? provenance
Sulfate boundaries
Separate the sulfate constituent from protonated forms, organic derivatives and complete host substances.
Referent boundary
Make explicit whether a name denotes sulfate itself, a reported sulfate pool or a sulfate-containing substance.
- Does the source use sulfate to mean free SO4^2−, an analytical total or a named sulfate salt? boundary
- Are hydrogen sulfate or organic sulfate esters present, and are they included in the reported result or represented separately? boundary
Sulfate host and form Locate sulfate within dissolved, solid and surface-associated pools.
The sulfate formula alone cannot determine mobility, availability or the behaviour of its host material.
Dissolved speciation
Describe sulfate in solution with the conditions needed to interpret protonation and ion association.
Aqueous sulfate pool
Distinguish an operational dissolved measurement from an estimate of free sulfate ions.
- What pH, temperature and solution composition accompany the dissolved sulfate record? measurement
- Does the value represent free sulfate, sulfate activity or a dissolved analytical total, and how was that interpretation obtained? definition
Solid and surface association
Identify sulfate-bearing phases and distinguish them from sulfate associated with surfaces or trapped solution.
Host phase identification
Record phase identity, relevant counterions and hydration without deriving a specific salt from sulfate detection alone.
- Which identified phases or surfaces host the sulfate, and what evidence distinguishes lattice sulfate from adsorbed sulfate or retained solution? provenance
- What counterions, phase proportions and hydration states are known well enough to interpret the solid's sulfate content? measurement
Sulfate quantity and evidence Make sulfate measurements interpretable and comparable.
Sulfate records can differ because of reporting basis, preparation and analytical selectivity even when their numerical units look similar.
Amount and reporting basis
Specify the numerator, denominator and sample fraction of every sulfate quantity.
Comparable sulfate quantity
Preserve enough information to convert or compare sulfate values without silently changing their meaning.
- Is the result expressed as SO4 mass, sulfur mass or amount of substance, and per what volume or material mass? measurement
- Which filtration, extraction, drying or other preparation defines the sulfate fraction and denominator being reported? boundary
Analytical confidence
Assess whether the method supports the claimed sulfate identity and quantity in this matrix.
Method fitness
Record method selectivity, uncertainty and sample treatment that could alter the sulfate result.
- Which method, calibration and quality-control evidence support the result, including detection limits and relevant matrix interferences? provenance
- Could collection, storage or preparation have produced sulfate from other sulfur species, dissolved a solid or removed sulfate from the measured fraction? boundary
Sulfate change Distinguish sulfate transfer between phases from chemical production or consumption.
A changing dissolved concentration does not establish whether sulfate has been removed from the system or chemically transformed.
Phase transfer
Track dissolution, precipitation, sorption and desorption involving sulfate.
Phase transfer assessment
Connect observed sulfate redistribution to named phases, conditions and evidence.
- Which sulfate-bearing phase or surface could account for the observed transfer, and what observations support that explanation? provenance
- Do measured concentrations and documented equilibrium assumptions indicate dissolution or precipitation potential, and what kinetic limits remain? measurement
Sulfur species conversion
Assess processes that form sulfate or convert it into other sulfur species.
Sulfate production or consumption
Require evidence for chemical conversion beyond a change in sulfate concentration.
- Which sulfur precursors or products were measured to support sulfate production or consumption? measurement
- What reaction conditions or biological evidence support the proposed conversion, and does a sulfur balance distinguish it from dilution or phase transfer? provenance
Sulfate interventions Connect sulfate evidence to feasible measurement, separation and handling decisions.
An agent must act on the actual sulfate-bearing material and track the consequences of changing its sulfate content.
Separation and removal
Evaluate interventions against the sulfate pool, treatment objective and receiving stream or phase.
Intervention fit
Specify what an intervention changes and where sulfate or its sulfur ends up.
- Is the objective to lower dissolved sulfate, remove sulfate-bearing solids, recover a salt or chemically convert sulfate? action
- Which candidate process fits the measured sulfate form and matrix, and what sulfate-bearing concentrate, solid or sulfur-containing product would it create? action
Material-specific use
Tie use and handling to the identified substance or mixture and verify the intervention outcome.
Use and outcome evidence
Prevent generic sulfate identity from substituting for material-specific information or a measured endpoint.
- Which identified salt or mixture, concentration, acidity and co-constituents determine whether the proposed use or handling is appropriate? action
- Which sulfate fraction and other affected constituents must be measured after intervention to demonstrate the intended result? measurement
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Aqueous sulfate ion (free SO₄²⁻ in solution)
- Hydrogen sulfate / bisulfate (HSO₄⁻)
- Inorganic sulfate salts (e.g. Na₂SO₄, CaSO₄, (NH₄)₂SO₄, MgSO₄, Al₂(SO₄)₃)
- Sulfate minerals (gypsum, anhydrite, barite, celestine, thenardite, alunite, jarosite)
- Organic sulfate esters (alkyl sulfates, steroid sulfates, sulfated glycosaminoglycans)
- Atmospheric and aerosol sulfate (H₂SO₄, NH₄HSO₄, (NH₄)₂SO₄ in particulate matter)
- Acid sulfate soils (actual versus potential, from sulfide oxidation)
- Coordinated sulfate (monodentate, bidentate or bridging ligand on metal centres)
- Which of these kinds and varieties hold for the sense of sulfate this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q172290 - Item for the sulfate anion SO₄²⁻.
- CAS Registry Number - 14808-79-8 - Sulfate ion; individual salts have their own CAS numbers.
- ChEBI - CHEBI:16189 - Chemical entity sulfate.
- PubChem CID - 1117 - Compound record for sulfate.
- IUPAC - tetraoxidosulfate(2−); sulfate - Red Book systematic name and accepted traditional name.
- InChIKey - QAOWNCQODCNURD-UHFFFAOYSA-L - Dianion; the -N key is the parent sulfuric acid.
- SMILES - [O-]S(=O)(=O)[O-] - Canonical representation of the free anion.
- Which of these identifiers and schemes hold for the sense of sulfate this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- WHO Guidelines for Drinking-water Quality (World Health Organization): sulfate treated as an aesthetic/laxative constituent rather than a health-based guideline value at usual concentrations.
- U.S. EPA National Secondary Drinking Water Regulations: secondary MCL 250 mg/L sulfate (aesthetic).
- Directive (EU) 2020/2184 (European Union): parametric value 250 mg/L sulphate in water intended for human consumption.
- ISO 10304-1 (International Organization for Standardization): ion-chromatographic determination of dissolved sulfate in water.
- ISO 9280 (International Organization for Standardization): gravimetric determination of sulfate with barium chloride.
- ASTM D516 (ASTM International): standard test method for sulfate ion in water.
- JECFA / Codex specifications (FAO/WHO): identity and purity of individual food-use sulfate salts (e.g. sodium, calcium, ammonium, magnesium sulfates).
- REACH and CLP (European Chemicals Agency / EU): registration and classification apply to named sulfate substances (the free ion is not itself a marketed substance); some metal sulfates (e.g. nickel sulfate) carry CMR classifications.
- Which of these standards and regulation hold for the sense of sulfate this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Dissolved sulfate is a major anion in seawater (~28 mmol/kg) and in many groundwaters and evaporite brines.
- Gypsum (CaSO₄·2H₂O) and anhydrite are bulk construction materials (plaster, plasterboard) and sources of sulfate scale.
- Ammonium sulfate is a nitrogen-and-sulfur fertilizer; sodium sulfate (salt cake) is used in kraft pulping, glass and detergents.
- Aluminium sulfate and related iron sulfates are coagulants in drinking-water and wastewater treatment.
- Barium sulfate is an insoluble radiocontrast agent and a weighting agent in drilling muds; magnesium sulfate is used medically as Epsom salt.
- Atmospheric sulfate, formed by oxidation of SO₂, is a large fraction of fine particulate matter and a driver of acid rain and aerosol climate forcing.
- In biochemistry, sulfate is activated as PAPS and transferred onto sugars, steroids and xenobiotics as sulfate esters.
- Sulfate-reducing microorganisms use SO₄²⁻ as a terminal electron acceptor in anoxic sediments, sewers and petroleum reservoirs.
- Which of these real-world use hold for the sense of sulfate this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Aqueous sulfate concentration (as SO₄) - drinking water commonly 0-250; seawater about 2700 - mg/L
- Seawater dissolved sulfate - 28.0-28.2 - mmol/kg
- Second acidity constant of sulfuric acid (HSO₄⁻ ⇌ H⁺ + SO₄²⁻) - 1.9-2.0 - pKa
- S-O bond length in the free tetrahedral anion - about 1.47 - Å
- Atmospheric sulfate in PM2.5 - remote air often <1; polluted urban/regional air commonly 1-15 - µg/m³ as SO₄
- Sulfur isotope composition δ³⁴S (source tracing) - commonly about −40 to +40 depending on source - ‰ versus VCDT
- Gypsum solubility in water at 25 °C - about 2.0-2.6 - g/L as CaSO₄·2H₂O
- Which of these typical measurements hold for the sense of sulfate this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- High-sulfate drinking water, especially as sodium or magnesium sulfate, causes osmotic diarrhea and a bitter or salty taste; this is the basis of the 250 mg/L aesthetic limits.
- Calcium sulfate scale (gypsum/anhydrite) fouls boilers, heat exchangers, oilfield tubing and reverse-osmosis membranes.
- External sulfate attack and thaumasite/ettringite formation degrade Portland-cement concrete in sulfate-bearing soils and groundwater.
- Oxidation of sulfide minerals in acid sulfate soils and mine waste generates sulfuric acid, mobilises metals and corrodes steel and concrete.
- Sulfate-reducing bacteria produce H₂S, sour oil and gas, and biogenic sulfuric acid that destroys sewer crowns.
- Secondary sulfate aerosol contributes to PM2.5 mortality risk and, as acid deposition, to ecosystem acidification.
- The sulfate ion itself is of low acute toxicity; hazard often tracks the cation (e.g. soluble barium, nickel or cadmium sulfates), not SO₄²⁻.
- Which of these failure modes and hazards hold for the sense of sulfate this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Spelling: IUPAC and U.S. usage is sulfate; British, Irish and much Commonwealth usage remains sulphate, including in EU drinking-water law.
- Acid sulfate soils are a named land-management problem in coastal Australia, the Mekong Delta, Florida, and Litorina clays of Finland and Sweden.
- Naturally high-sulfate groundwater is characteristic of evaporite and arid basins (parts of the North American Great Plains, interior Australia, some Mediterranean and Central Asian aquifers).
- Mineral-class naming of sulfates (gypsum versus alabaster versus selenite; baryte versus barite) still follows national mineralogical traditions.
- Which of these regional variation hold for the sense of sulfate this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- sulfite (SO₃²⁻) - Sulfur(IV) versus sulfur(VI); sulfite is a reductant (iodine, dichromate) and is oxidised to sulfate; ion chromatography or a selective oxidation step separates them.
- sulfide / hydrogen sulfide (S²⁻, H₂S) - Sulfur(−II); acid-volatile, odorous, precipitated as metal sulfides; not retained as sulfate on anion chromatography without prior oxidation.
- thiosulfate (S₂O₃²⁻) - Contains an S-S linkage and titrates iodine; distinct IC retention and no BaSO₄ precipitate until oxidised.
- peroxydisulfate / persulfate (S₂O₈²⁻) - Peroxo-bridged S(VI) dimer and a strong oxidant; not the free sulfate ion, though it hydrolyses or is reduced to sulfate.
- organosulfonate (R-SO₃⁻) - C-S bond, not the C-O-S of a sulfate ester; sulfonates resist acid hydrolysis that cleaves sulfate esters to SO₄²⁻.
- hydrogen sulfate / bisulfate (HSO₄⁻) - The monoprotonated form of the same acid system; dominates only at low pH (around and below pKa ≈ 2) and is readily distinguished by charge and pH.
- phosphate (PO₄³⁻) - Analogous tetrahedral oxoanion of phosphorus; molybdenum-blue colorimetry, ³¹P NMR, or ion chromatography separate it from sulfate.
- selenate (SeO₄²⁻) - Isostructural selenium(VI) analogue; not precipitated quantitatively as BaSO₄ under the same conditions and is measured by selenium-specific spectroscopy or IC.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of sulfate this model covers, and on what evidence? provenance
Sources
- Nomenclature of Inorganic Chemistry, IUPAC Recommendations 2005 (the Red Book) - Systematic name tetraoxidosulfate(2−) and the accepted name sulfate for the SO₄²⁻ anion.
- PubChem Compound Summary for CID 1117, Sulfate - CAS 14808-79-8, InChIKey, formula, and identifier crosswalk for the sulfate ion.
- ChEBI CHEBI:16189 sulfate - Chemical-entity identity of sulfate as an inorganic anion and its parentage to sulfuric acid.
- Chemistry of the Elements, 2nd edition - Structure, acid-base behaviour of HSO₄⁻/SO₄²⁻, and the mineral and industrial chemistry of sulfate salts.
- Guidelines for Drinking-water Quality, 4th edition incorporating the first and second addenda - Taste and laxative effects of sulfate in drinking water and the absence of a health-based guideline at concentrations usually found.
- National Secondary Drinking Water Regulations: sulfate SMCL 250 mg/L - U.S. secondary maximum contaminant level of 250 mg/L sulfate as an aesthetic/nuisance standard.
- Directive (EU) 2020/2184 on the quality of water intended for human consumption - EU parametric value of 250 mg/L for sulphate in drinking water.
- ISO 10304-1: Water quality - Determination of dissolved anions by liquid chromatography of ions - Part 1 - Standard ion-chromatographic determination of dissolved sulfate in water.
What the second pass must settle
- Does the registry intend sulfate to denote only inorganic SO4^2−, or also sulfate salts, hydrogen sulfate and organic sulfate derivatives?
- Does an existing Vercy world model already own this concept or a broader sulfur-speciation model to which this entry should link?
- Which sample matrices and intended decisions should determine the initial analytical methods and evidence requirements?
- Which authoritative thermodynamic sources and activity models should support sulfate speciation and sulfate-mineral saturation assessments across the intended conditions?
- Which application-specific criteria should govern intervention success, and which neighbouring models should own those criteria?