Industrial grade 40% 96% Ferric chloride CAS 7705-08-0

What is Ferric Chloride? How does it work?

Ferric Chloride, also known as iron(III) chloride, iron trichloride, iron chloride, ferric trichloride, Flores martis, has the chemical formula FeCl3, a molecular weight of 162.20, CAS number 7705-08-0 (hexahydrate 10025-77-1), EINECS 231-729-4, UNII U38V3ZVV3V, InChIKey RBTARNINKXHZNM-UHFFFAOYSA-K, ICSC 1499, UN 1773 (solid)/UN 2582 (solution). It is an ionic iron salt composed of trivalent iron ions (Fe³⁺) and three chloride ions (Cl⁻), belonging to the trivalent iron halide class. It is the world's most widely used iron-based water treatment agent and etching chemical: at room temperature, it is an orange-brown to brownish-black crystal (anhydrous) or yellow-brown crystal (hexahydrate), non-flammable, and extremely soluble in water (dissolution is exothermic, the aqueous solution is yellow-brown, strongly acidic, and hydrolyzes to produce ferric hydroxide precipitate). It decomposes in the molten state at approximately 304℃ and 316℃, and in the wet state, it is corrosive to aluminum and most metals. Due to its properties such as hydrolysis flocculation, chemical precipitation, redox reaction, Lewis acid catalysis, and coordination color development, industrial-grade ferric chloride is mainly used in drinking water and sewage treatment, industrial wastewater treatment, printed circuit board etching, metal etching, catalysts, fine chemical synthesis, pigment raw materials, and analytical reagents.

Basic identification information : Chemical formula FeCl3 (Cl3Fe); Molecular weight 162.20; CAS number 7705-08-0 (anhydrous), 10025-77-1 (hexahydrate); EINECS 231-729-4; UNII U38V3ZVV3V; InChIKey RBTARNINKXHZNM-UHFFFAOYSA-K; IUPAC name trichloroiron; ChEBI 30808; ICSC 1499; UN 1773 (solid)/2582 (solution); Aliases: ferric chloride, iron(III) chloride, iron trichloride, iron chloride, ferric trichloride, Flores martis, etc.

Structurally , ferric chloride is composed of ferric ions and three chloride ions through ionic bonds (partial covalentity and layered lattice in the solid phase); the anhydrous form is a dark brown hexagonal crystal, while the hexahydrate is a yellow-brown crystal.

Physically , ferric chloride is an orange-brown to brownish-black or yellow-brown crystal; its anhydrous form has a melting point of approximately 304°C and decomposes at approximately 316°C (releasing chlorine gas); its density is approximately 2.9 g/cm³; it is extremely soluble in water (dissolution is significantly exothermic), soluble in ethanol, ether, and acetone; its aqueous solution is yellow-brown and becomes strongly acidic due to hydrolysis; it is highly hygroscopic and deliquesces upon exposure to air; it is non-flammable.

Chemically , ferric chloride is a strongly acidic ferric salt:it exhibits pronounced solubility and hydrolysis in aqueous solutions, leading to the formation of polynuclear ferric hydroxy complexes and brownish-red ferric hydroxide colloids with the release of hydrogen ions; ferric ions are moderate oxidants, capable of oxidizing copper, hydrogen sulfide, iodide ions etc. (to ferrous ions), which underpins its etching and oxidation properties; as a Lewis acid, ferric ions have vacant orbitals for accepting electron pairs, facilitating various organic reactions; ferric ions interact with thiocyanate, phenolic hydroxyl groups etc. to generate characteristic color complexes for analysis and detection; ferric ions can generate insoluble precipitates with phosphate, arsenate etc., used for phosphorus and arsenic removal; it exhibits astringent and protein-coagulating effects on skin and mucous membranes.

Why does ferric chloride play these roles in various industrial fields? Its mechanism of action mainly includes the following:

Hydrolysis flocculation mechanism : Trivalent iron ions hydrolyze in water to generate polynuclear hydroxy iron complexes and positively charged ferric hydroxide colloids, which neutralize the negative charge of colloidal particles in the water, compress the double electric layer to destabilize them, and then aggregate fine suspended matter into large flocs and settle through adsorption bridging and netting sweeping action. This is the core principle of its use as a flocculant to purify water.

Chemical precipitation and phosphorus removal mechanism : Ferric ions react with anions such as phosphate and arsenate to form insoluble precipitates of ferric phosphate and ferric arsenate, converting dissolved phosphorus and arsenic in water into solid phases for removal. Combined with flocculation and sedimentation, this achieves phosphorus removal in wastewater and arsenic removal in drinking water.

Redox mechanism : Ferric ions are moderately strong oxidants that can oxidize copper (2Fe³⁺ + Cu → 2Fe²⁺ + Cu²⁺), hydrogen sulfide, iodide ions, etc., and then reduce themselves to ferrous ions. This is the chemical basis for etching copper foil, removing hydrogen sulfide odor and oxidizing some organic pollutants.

Lewis acid catalysis mechanism : Trivalent iron ions have empty orbitals and can accept electron pairs. They are typical Lewis acids, which can activate substrates, promote electrophilic reactions and reactions such as chlorination, polymerization, and coupling, and act as catalysts or co-catalysts for organic synthesis and polymerization reactions.

Coordination colorimetric mechanism : Ferric ions form blood-red complexes with thiocyanate, purple complexes with phenols, and Prussian blue precipitates with potassium ferrocyanide. These characteristic colorimetric reactions can be used for qualitative and quantitative analysis of iron and various other substances.

 All Uses of Industrial-Grade Ferric Chloride

1. Drinking water purification flocculant (municipal water treatment industry)

Corresponding products: drinking water flocculants, municipal water supply treatment agents, coagulation and sedimentation agents, raw water clarifiers, arsenic and fluoride removal agents, water plant purification agents, emergency water purification agents, etc.

Why it works for this purpose: Ferric chloride hydrolyzes to produce ferric hydroxide colloids which neutralize and capture suspended solids, colloids, and algae in the water, causing a rapid decrease in turbidity and color. At the same time, ferric iron reacts with arsenic and fluorine to form precipitates, achieving the removal of arsenic and fluorine. It is a commonly used flocculant in municipal drinking water treatment, except for aluminum-based flocculants. Its effectiveness is less affected by pH, and it produces large and dense flocs.

2. Wastewater treatment and industrial wastewater treatment agents (municipal/industrial wastewater treatment)

Corresponding products: flocculants for domestic sewage, phosphorus removal agents, sludge conditioners, sludge dewatering agents, sewage decolorizing agents, decolorizing agents for dyeing and printing wastewater, heavy metal removal agents for electroplating wastewater, wastewater treatment agents for papermaking, flocculants for chemical wastewater, phosphorus removal agents for phosphorus-containing wastewater, wastewater treatment agents for food processing, wastewater treatment agents for mining, etc.

Why it works for this purpose:Ferric chloride is used as a flocculating agent in the treatment of sewage and industrial waste water to remove suspended matter and organic colloids. Ferric phosphate precipitate is formed by the ferric iron to achieve chemical phosphorus removal. It can also co-precipitate with heavy metals to remove metal ions such as, copper, chromium, zinc. Decolorization is achieved by hydrolysis and flocculation which remove dyes. Meanwhile, it is able to be used as a sludge conditioner to improve the performance of sludge dewatering and increase the dewatering efficiency. It is a multi-effect treatment agent in the municipal and industrial wastewater treatment plants.

3. Metal Etching Agents (Electronics/Metal Processing/Printing Industry)

Corresponding products:PCB etching solution, circuit board etchant, copper foil etching solution, electronic class ferric chloride etching solution, flexible board etching solution, nameplate etchant, precision parts etching solution, stainless steel etchant, photolithography etching solution, engraving etchant, printing screen etchant, etc.

Why it works for this purpose:  Ferric ions oxidize metallic copper to produce soluble copper chloride and ferrous chloride (2Fe³⁺ + Cu → 2Fe²⁺ + Cu²⁺), selectively etching away unprotected copper foil to produce circuit patterns; it also etches patterns and textures on the surface of nameplates, precision parts and metal plates by controlled oxidation and dissolution. It is a traditional wet etchant used in circuit board production and also in metal etching processes with controllable etching rate and low cost.

4. Lewis acid catalysts (chemical catalysis industry)

Corresponding products: chlorination reaction catalysts, polymerization catalysts, Friedel-Crafts reaction catalysts, organic synthesis catalytic systems, esterification catalyst aids, condensation reaction catalysts, wastewater oxidation catalysts, etc.

Why it works for this purpose:Trivalent iron ions have empty orbitals and are typical Lewis acids. They can accept substrate electron pairs, activate carbonyl groups and halogens, and promote reactions such as chlorination, alkylation, acylation, polymerization and condensation. They can be used as catalysts or co-catalysts for organic synthesis and polymer polymerization. They are also inexpensive and easy to separate.

5. Oxidizing agents and reagents for fine chemical synthesis (fine chemical industry)

Corresponding products: organic oxidants, nitro reduction auxiliaries, dye synthesis reagents, chlorination reagents, oxidative dehydrogenation reagents, organic synthesis catalyst systems, etc.

Why it works for this purpose:Ferric ions are mild and controllable oxidants that can oxidize the substrate (and reduce themselves to ferrous ions). They are used for organic transformations such as nitro reduction, oxidative coupling, and dehydrogenation. They can also be used as reagents for chlorination and oxidation reactions. They are commonly used iron salts in fine chemicals.

6. Iron oxide pigments and raw materials for iron-based materials (pigment/materials industry)

Corresponding products: iron oxide red pigment, iron oxide yellow pigment, iron oxide black pigment, iron-based magnetic materials, ferrite raw materials, ceramic colorants, building material colorants, pigment intermediates, etc.

Why it works for this purpose:Ferric chloride is a high-purity iron source for preparing iron oxide pigments and iron-based materials. Through processes such as precipitation, oxidation, and calcination, it is converted into iron oxide red, yellow, black and other pigments and ferrite magnetic materials, which are widely used in coatings, building materials, ceramics and magnetic products.

7. Chemical analysis reagents (analytical chemical industry)

Corresponding products: iron content determination reagents, ferric thiocyanate colorimetric reagents, phenol detection reagents, qualitative analysis reagents, indicator matching reagents, colorimetric analysis standard reagents, water quality analysis reagents, etc.

Why it works for this purpose:The characteristic colorimetric reactions of ferric ions with thiocyanate to form a blood-red complex and with phenols to form a purple complex can be used for the qualitative and quantitative analysis of substances such as iron, thiocyanate, and phenols. It is a commonly used analytical colorimetric reagent in the laboratory.

Summarize

Ferric chloride (CAS 7705-08-0) is a trivalent iron salt composed of iron and chlorine. Its core properties are hydrolysis and flocculation of ferric ions, chemical precipitation, redox reactions, Lewis acid catalysis, and coordination colorimetry. Industrially, it is mainly used in drinking water and municipal wastewater treatment (flocculation, phosphorus removal, sludge conditioning), industrial wastewater treatment (decolorization, heavy metal removal), printed circuit board etching, metal etching and plate making, Lewis acid catalysis, fine chemical synthesis, iron oxide pigment preparation, and analytical reagents. Understanding the hydrolysis chemistry and redox properties of ferric ions explains why it can flocculate and purify water, etch copper foil, and catalyze synthesis and colorimetric detection—this is its versatility across water treatment, electronics, chemical engineering, and materials science.