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HEDP

CAS No. : 2809-21-4
EC No. : 220-552-8

Synonyms:
Etidronic acid; Didronel; 1-Hydroxyethane 1,1-diphosphonic acid; HEDP; Etidronic acid; etidronate; 2809-21-4; 1-Hydroxyethylidene-1,1-diphosphonic acid; EHDP; HEDP drum; Etidronsaeure; Acetodiphosphonic acid; Hydroxyethanediphosphonic acid; Didronel; Turpinal SL; Oxyethylidenediphosphonic acid; Dequest 2015; Dequest Z 010; Acido etidronico; Ferrofos 510; Acide etidronique; 1-Hydroxyethane-1,1-diphosphonate; 1-Hydroxyethane-1,1-diphosphonic acid; Phosphonic acid, (1-hydroxyethylidene)bis-; Diphosphonate (base); (1-Hydroxyethane-1,1-diyl)diphosphonic acid; 1-Hydroxyethanediphosphonic acid; Dequest 2010; Ethane-1-hydroxy-1,1-diphosphonic acid; (Hydroxyethylidene)diphosphonic acid; Ethane-1-hydroxy-1,1-diphosphonate; (1-Hydroxyethylene)diphosphonic acid; Acide etidronique [INN-French]; Acido etidronico [INN-Spanish]; Acidum etidronicum [INN-Latin]; (1-Hydroxyethylidene)diphosphonic acid; 1,1,1-Ethanetriol diphosphonate; 1-Hydroxyethylidene-1,1-bisphosphonate; 1-Hydroxyethane-1,1-bisphosphonic acid; 1-HYDROXY-1,1-DIPHOSPHONOETHANE; (1-Hydroxyethylidene)bis(phosphonic acid); Acidum etidronicum; (1-Hydroxyethylidene)bisphosphonic acid; (1-hydroxyethane-1,1-diyl)bis(phosphonic acid); Hydroxyethane-1,1-diphosphonic acid; 1000SL; (1-Hydroxyethylidene)diphoshonic acid; Etidronic acid [USAN:INN:BAN]; RP 61; (1-hydroxy-1-phosphonoethyl)phosphonic acid; 1-Hydroxyethylidene-1,1-biphosphonate; Phosphonic acid, (1-hydroxyethylidene)di-; EINECS 220-552-8; Ethane-1-hydroxy-1,1-bisphosphonate; Phosphonic acid, 1-hydroxy-1,1-ethanediyl ester; BRN 1789291; M2F465ROXU; ethane-1-hydroxy-1,1-bisphosphonic acid; 2809-21-4 (freeacid); (1-hydroxy-1-phosphono-ethyl)phosphonic acid; 1-hydroxyethane 1,1-diphosphonic acid; NSC-227995; 1-HydroxyEthylidene-1,1-DiphosphonicAcid; (1-hydroxyethan-1,1-diyl)bis(phosphonic acid); (1-Hydroxy-1,1-ethanediyl)bis(phosphonic acid); Phosphonic acid, P,P'-(1-hydroxyethylidene)bis-; NCGC00159352-02; Etidronic acid (USAN/INN); C2H8O7P2; 1-Hydroxyethylidenediphosphonic acid; 1-hydroxy ethylidene; HDEPA; OEDFK; Etidronate (Didronel); EC 220-552-8; 0-02-00-00171 (Beilstein Handbook Reference); GTPL7184; Etidronic acid 2809-21-4; Etidronic acid 60% aqueous solution; NSC227995; s1857; STK721995; AKOS005524039; Etidronic acid, 60% aqueous solution; Etidronic acid; Didronel; 1-Hydroxyethane 1,1-diphosphonic acid; HEDP; Etidronic acid; etidronate; 2809-21-4; 1-Hydroxyethylidene-1,1-diphosphonic acid; EHDP; Etidronsaeure; Acetodiphosphonic acid; Hydroxyethanediphosphonic acid; Didronel; Turpinal SL; Oxyethylidenediphosphonic acid; Dequest 2015; Dequest Z 010; Acido etidronico; Ferrofos 510; (1-hydroxy-ethylidene)diphosphonic acid; SC-25504; 1-hydroxyethane-1,1-diyldiphosphonic acid; CAS-2809-21-4; 1-hydroxy ethylidene-1,1-diphosphonic acid; LS-106637; FT-0607934; FT-0668439; (1-Hydroxy-1-phosphono-ethyl)-phosphonic acid; (1-Hydroxyethylidene)bisphosphonic acid monohydrate; 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (Powder); (1-Hydroxyethane-1,1-diyl)diphosphonic acid monohydrate; 1-Hydroxyethylidenediphosphonic acid 60% aqueous solution; 1-Hydroxyethane-1,1,-diphosphonic acid 60% aqueous solution; 1-Hydroxyethane-1,1-diphosphonic acid; 1-Hydroxyethylidene-1,1-diphosphonic acid; 1-hydroxyethylidenedi(phosphonic acid); Etidronic Acid; 1-Hydroxyethylidene-1,1-bis-(phosphonic acid); Ethane-1-hydroxy-1,1-diphosphonic acid; 1-Hydroxy-1,1-diphosphonoethane; Oxyethylidenediphosphonic acid

HEDP

HEDP , also known as etidronate, is a bisphosphonate used as a medication, detergent, water treatment, and cosmetic.
It was patented in 1966 and approved for medical use in 1977.

Use
Medical
HEDP is a bisphosphonate used to strengthen bone, treat osteoporosis, and treat Paget's disease of bone.
Bisphosphonates primarily reduce osteoclastic activity, which prevents bone resorption, and thus moves the bone resorption/formation equilibrium toward the formation side and hence makes bone stronger on the long run. Etidronate, unlike other bisphosphonates, also prevents bone calcification. For this reason, other bisphosphonates, such as alendronate, are preferred when fighting osteoporosis. To prevent bone resorption without affecting too much bone calcification, etidronate must be administered only for a short time once in a while, for example for two weeks every 3 months. When given on a continuous basis, say every day, etidronate will altogether prevent bone calcification. This effect may be useful and etidronate is in fact used this way to fight heterotopic ossification. But in the long run, if used on a continuous basis, it will cause osteomalacia.

Chemical
Main article: Corrosion inhibitor
HEDP is used as a retardant in concrete, scale and corrosion inhibition in circulating cool water system, oil field and low-pressure boilers in fields such as electric power, chemical industry, metallurgy, fertilizer, etc. In light woven industry, HEDP is used as detergent for metal and nonmetal. In dyeing industry, HEDP is used as peroxide stabilizer and dye-fixing agent; In non-cyanide electroplating, HEDP is used as chelating agent. The dosage of 1–10 mg/L is preferred as scale inhibitor, 10–50 mg/L as corrosion inhibitor, and 1000–2000 mg/L as detergent. Usually, HEDP is also used together with polycarboxylic acid (superplasticizer), in which it acts as reducing agent.

Chelating agent and antioxidant
HEDP is a chelating agent and may be added to bind or, to some extent, counter the effects of substances, such as calcium, iron or other metal ions, which may be discharged as a component of grey wastewater and could conceivably contaminate groundwater supplies. As a phosphonate it has corrosion inhibiting properties on unalloyed steel. HEDP also acts to retard rancidification and oxidation of fatty acids.
HEDP and its salts are added to detergents and other cleaning agents to prevent the effects of hard water. It is also used in peroxide bleaching to prevent degradation of peroxides by transition metals.
HEDP is listed as an ingredient of several cosmetic formulations where it is used for suppressing radical formation, emulsion stabiliser and viscosity control. While HEDP has not been limited from inclusion in cosmetics and does have legitimate uses, it is recommended that, as with most cosmetic products (particularly soaps), the product should be thoroughly rinsed from the skin after use.
HEDP is also included among swimming pool chemicals. It is used as a stain inhibitor to prevent metal ions coming out of solution and staining the sides of swimming pools.

Pharmacology
Relative potency
Bisphosphonate Relative potency
Etidronate 1
Tiludronate 10
Pamidronate 100
Alendronate 100-500
Ibandronate 500-1000
Risedronate 1000
Zoledronate 5000
Synthesis
HEDP can be prepared by reaction of Phosphorus trichloride with acetic acid in a tertiary amine, or by reaction of an acetic acid/acetic anhydride mixture with phosphorous acid.

A HEDP is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy, that comes into contact with the fluid.[1] The effectiveness of a HEDP depends on fluid composition, quantity of water, and flow regime. HEDP s are common in industry, and also found in over-the-counter products, typically in spray form in combination with a lubricant and sometimes a penetrating oil. They may be added to water to prevent leaching of lead or copper from pipes.[2]
A common mechanism for inhibiting corrosion involves formation of a coating, often a passivation layer, which prevents access of the corrosive substance to the metal. Permanent treatments such as chrome plating are not generally considered inhibitors, however: HEDP s are additives to the fluids that surround the metal or related object.

Types
Benzotriazole inhibits corrosion of copper by forming an inert layer of this polymer on the metal's surface
The nature of the corrosive inhibitor depends on (i) the material being protected, which are most commonly metal objects, and (ii) on the corrosive agent(s) to be neutralized. The corrosive agents are generally oxygen, hydrogen sulfide, and carbon dioxide. Oxygen is generally removed by reductive inhibitors such as amines and hydrazines:
O2 + N2H4 → 2 H2O + N2
In this example, hydrazine converts oxygen, a common corrosive agent, to water, which is generally benign. Related inhibitors of oxygen corrosion are hexamine, phenylenediamine, and dimethylethanolamine, and their derivatives. Antioxidants such as sulfite and ascorbic acid are sometimes used. Some HEDP s form a passivating coating on the surface by chemisorption. Benzotriazole is one such species used to protect copper. For lubrication, zinc dithiophosphates are common - they deposit sulfide on surfaces.
The suitability of any given chemical for a task in hand depends on many factors, including their operating temperature.

Illustrative applications
Volatile amines are used in boilers to minimize the effects of acid. In some cases, the amines form a protective film on the steel surface and, at the same time, act as an anodic inhibitor. An inhibitor that acts both in a cathodic and anodic manner is termed a mixed inhibitor.
Benzotriazole inhibits the corrosion and staining of copper surfaces.[3]
HEDP s are often added to paints. A pigment with anticorrosive properties is zinc phosphate. Compounds derived from tannic acid or zinc salts of organonitrogens (e.g. Alcophor 827) can be used together with anticorrosive pigments. Other HEDP s are Anticor 70, Albaex, Ferrophos, and Molywhite MZAP.

In a perinatal and postnatal study, pregnant female Long-Evans rats (20/group, except 21/high-dose group) were orally exposed by gavage to HEDP at dose levels of 16.51, 110.09, or 330.28 mg/kg/day (in one-half doses, twice daily in deionized water; 10 ml/kg/day) on gestation day (GD) 15 through the end of gestation and the period of lactation. Surviving animals were sacrificed on lactation day 21. Significant differences were observed between treated and control animals in the following: decreased implantations/dam (high-dose group), decreased live fetuses/total fetuses (low-dose group), increased pup survival (lactation days 0-4, high-dose group), increased pup body weight (high- and mid-dose groups), and decreased number of females (mid-dose group). No significant differences were observed between treated and control animals in the following: pregnancy rate, length of gestation period, number of litters delivered, maternal weight gain, mortality, physical observations, or necropsy observations, numbers of pups/dam, live or dead fetuses/litter, live fetuses/implantation, pup sex ratios, and gross pup necropsy observations.

Teratogenicity was evaluated in pregnant Long-Evans rats (20/group) orally exposed by gavage to HEDP at dose levels of 0, 16.51, 110.09 or 330.28 mg/kg/day (in deionized water solutions, 10 ml/kg/day, one-half doses given twice daily) on gestation days (GD) 6-15. All surviving rats were sacrificed on GD 20. Significant differences were observed between treated and control animals with respect to a decreased incidence of soft tissue abnormalities (low-dose group). No significant differences were observed between treated and control animals in the following: maternal mortality, body weight, body weight change, pregnancy rate, physical observations, numbers of corpora lutea, implantations, live fetuses, resorptions, implantation frequency, necropsy observations, percent viable or resorbed fetuses, fetal weight, crown-rump length, sex ratio, ossification variations, and skeletal malformations.

Antiseptics are used to counter microbial corrosion. Benzalkonium chloride is commonly used in oil field industry.
In oil refineries, hydrogen sulfide can corrode steels so it is removed often using air and amines by conversion to polysulfides.
Orthophosphates may be added in water treatment systems to prevent leaching of lead and copper from pipes.[2]
Fuels industry
HEDP s are commonly added to coolants, fuels, hydraulic fluids, boiler water, engine oil, and many other fluids used in industry. For fuels, various HEDP s can be used. Some components include zinc dithiophosphates.
DCI-4A, widely used in commercial and military jet fuels, acts also as a lubricity additive. Can be also used for gasolines and other distillate fuels.
DCI-6A, for motor gasoline and distillate fuels, and for U.S. military fuels (JP-4, JP-5, JP-8)
DCI-11, for alcohols and gasolines containing oxygenates
DCI-28, for very low-pH alcohols and gasolines containing oxygenates
DCI-30, for gasoline and distillate fuels, excellent for pipeline transfers and storage, caustic-resistant
DMA-4 (solution of alkylaminophosphate in kerosene), for petroleum distillates

With the involvement of high-end technology, modern machinery and advanced tools in all our processes, we are engaged in offering HEDP (35 Liters). Manufactured by our experts in fulfillment with international quality standards using high quality raw materials, these s are designed with high precision. These HEDP s are provided in various sizes & capacity according to the needs of customers. Also, our quality controllers test these s on various parameters and ensure that only best range is supplied to the market.

Features:
Accord proper protection
Dimensionally accurate
Tamper resistant

Specifications:
Material HM/HEDP
Diameter 325 mm
Height 540 mm
Mouth Opening ID 250 mm
Overflow Capacity 37 Liter
Weight 1.8 kg./2.0 kg

HEDP is indicated to treat Paget's disease of bone, as well as the treatment and prevention of heterotropic ossification after total hip replacement of spinal cord injury.
HEDP - REG, May only be used with peroxyacetic acid, < 4.8 ppm in wash water for fruits & vegs that are not raw agricultural commodities- 173.315.
HEDP is a first generation bisphosphonate that inhibits the action of osteoclasts, preventing bone resporption.[L13901] It has a wide therapeutic index as overdoses are not associated with severe toxicity and a long duration of action as it slowly releases from the bone.[L13901] Patients should be counselled regarding the risk of upper gastrointestinal adverse reactions.

As a member of the family of drugs known as bisphosphonates, HEDP differs from endogenous pyrophosphate in its resistance to enzymatic hydrolysis. This agent adsorbs to hydroxyapatite cells and reduces the number of osteoclasts, thereby inhibiting abnormal bone resorption. HEDP may also directly stimulate bone formation by osteoblasts.
HEDP has an oral bioavailability of 1-10%.[A203357] Further data regarding pharmacokinetics of HEDP are not readily available.
Absorbed HEDP is eliminated in the urine, while the unabsorbed drug is eliminated in the feces.
HEDP has a volume of distribution of 0.3-1.3L/kg.

HEDP is a bisphosphonate used to strengthen bone, treat osteoporosis, and treat Paget's disease of bone.
Bisphosphonates primarily reduce osteoclastic activity, which prevents bone resorption, and thus moves the bone resorption/formation equilibrium toward the formation side and hence makes bone stronger on the long run. Etidronate, unlike other bisphosphonates, also prevents bone calcification. For this reason, other bisphosphonates, such as alendronate, are preferred when fighting osteoporosis. To prevent bone resorption without affecting too much bone calcification, etidronate must be administered only for a short time once in a while, for example for two weeks every 3 months. When given on a continuous basis, say every day, etidronate will altogether prevent bone calcification. This effect may be useful and etidronate is in fact used this way to fight heterotopic ossification. But in the long run, if used on a continuous basis, it will cause osteomalacia.

Application
Etidronic acid monohydrate also known as 1-hydroxyethylidenediphosphonic acid (HEDP ) is an organophosphonic acid that can be used to surface functionalize NaY molecular sieves. HEDP/NaY can be used as a catalyst for n-butyl acetate production via esterification.[2]
HEDP can be also employed as a chelating agent in the synthesis of metal-ligand complexes.

Etidronic acid (HEBP) can be employed as a catalyst for the synthesis of:
• 5-Nitro-3,4-dihydropyrimidin-2(1H)-ones through the reaction between 1-(2-hydroxyphenyl)-2-nitroethanone, aryl aldehydes and urea via one-pot cyclo condensation reaction.[1]
• Thiiranes from epoxides and ammonium thiocyanate.

About HEDP
Helpful information
HEDP is registered under the REACH Regulation and is manufactured in and / or imported to the European Economic Area, at ≥ 10 000 to < 100 000 per annum.
HEDP is used by consumers, in articles, by professional workers (widespread uses), in formulation or re-packing, at industrial sites and in manufacturing.

Consumer Uses
HEDP is used in the following products: water softeners, washing & cleaning products, air care products, polishes and waxes, coating products, fertilisers and cosmetics and personal care products.
Other release to the environment of HEDP is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners) and outdoor use.
Article service life
Release to the environment of HEDP can occur from industrial use: in the production of articles and in processing aids at industrial sites. Other release to the environment of HEDP is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners), outdoor use resulting in inclusion into or onto a materials (e.g. binding agent in paints and coatings or adhesives) and indoor use in long-life materials with low release rate (e.g. flooring, furniture, toys, construction materials, curtains, foot-wear, leather products, paper and cardboard products, electronic equipment). HEDP can be found in complex articles, with no release intended: machinery, mechanical appliances and electrical/electronic products (e.g. computers, cameras, lamps, refrigerators, washing machines) and vehicles. HEDP can be found in products with material based on: stone, plaster, cement, glass or ceramic (e.g. dishes, pots/pans, food storage containers, construction and isolation material), metal (e.g. cutlery, pots, toys, jewellery), wood (e.g. floors, furniture, toys), fabrics, textiles and apparel (e.g. clothing, mattress, curtains or carpets, textile toys) and paper (e.g. tissues, feminine hygiene products, nappies, books, magazines, wallpaper).

Widespread uses by professional workers
HEDP is used in the following products: water softeners, coating products, washing & cleaning products, air care products, polishes and waxes, fertilisers and cosmetics and personal care products.
HEDP is used in the following areas: building & construction work and agriculture, forestry and fishing.
Release to the environment of HEDP can occur from industrial use: in the production of articles.
Other release to the environment of HEDP is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners) and outdoor use.
Formulation or re-packing
HEDP is used in the following products: pH regulators and water treatment products, water softeners, water treatment chemicals and washing & cleaning products.
Release to the environment of HEDP can occur from industrial use: formulation of mixtures, formulation in materials, manufacturing of the substance and in processing aids at industrial sites.

Uses at industrial sites
HEDP is used in the following products: water softeners, pH regulators and water treatment products, water treatment chemicals, washing & cleaning products and coating products.
HEDP is used in the following areas: municipal supply (e.g. electricity, steam, gas, water) and sewage treatment, mining and formulation of mixtures and/or re-packaging.
HEDP is used for the manufacture of: pulp, paper and paper products, textile, leather or fur, metals, fabricated metal products, machinery and vehicles, furniture and chemicals.
Release to the environment of HEDP can occur from industrial use: in processing aids at industrial sites, in the production of articles and as processing aid.
Other release to the environment of HEDP is likely to occur from: indoor use (e.g. machine wash liquids/detergents, automotive care products, paints and coating or adhesives, fragrances and air fresheners).

Manufacture
Release to the environment of HEDP can occur from industrial use: manufacturing of the substance, formulation of mixtures and in processing aids at industrial sites.
HEDP is a first generation bisphosphonate similar to clodronic acid and tiludronic acid.1 These drugs were developed to mimic the action of pyrophosphate, a regulator of calcification and decalcification.4 Etidronate’s use has decreased over the years in favor of the third generation, nitrogen containing bisphosphonate zoledronic acid, ibandronic acid, minodronic acid, and risedronic acid.

Pharmacodynamics
HEDP is a first generation bisphosphonate that inhibits the action of osteoclasts, preventing bone resporption.7 It has a wide therapeutic index as overdoses are not associated with severe toxicity and a long duration of action as it slowly releases from the bone.7 Patients should be counselled regarding the risk of upper gastrointestinal adverse reactions.

Mechanism of action
Bisphosphonates are taken into the bone where they bind to hydroxyapatite. Bone resorption by osteoclasts causes local acidification, releasing the bisphosphonate, which is taken into the osteoclast by fluid-phase endocytosis.2 Endocytic vesicles become acidified, releasing bisphosphonates into the cytosol of osteoclasts where they act.2
Osteoclasts mediate resorption of bone.3 When osteoclasts bind to bone they form podosomes, ring structures of F-actin.3 Disruption of the podosomes causes osteoclasts to detach from bones, preventing bone resorption.3
First generation bisphosphonates closely mimic the structure of pyrophosphate, which can be incorporated into ATP anologues that cannot be hydrolyzed, disrupting all ATP mediated actions of osteoclasts.

Absorption
HEDP has an oral bioavailability of 1-10%.5 Further data regarding pharmacokinetics of HEDP are not readily available.5,7
Volume of distribution
HEDP has a volume of distribution of 0.3-1.3L/kg.5

Protein binding
Not Available
Metabolism
HEDP is not metabolized in vivo

Route of elimination
Absorbed HEDP is eliminated in the urine, while the unabsorbed drug is eliminated in the feces.7
Half-life
The half life of etidronate is approximately 1-6 hours.5,7
Clearance
HEDP has a renal clearance of 0.09L/kg/h.

1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP ) acid with its CAS number 2809-21-4 is a cost effective scale inhibitor used in various industrial applications such as industrial water treatment and detergents.
1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP ) further shows good stability in presence of chlorine as well as corrosion inhibition properties in presence of zinc and other phosphates and can also be used as chelating agent in the textile industry.

Main Applications for HEDP are
Cooling water systems / industrial water treatment
Industrial detergents
Swimming pools
Metal surface treatment as a corrosion inhibitor for steel
Stabilizer in H2O2 solutions
Sequestering agent in textile auxiliaries

Packaging & Shelf Life
s of 250kg net
IBCs / totes of 1.250kg net
Bulk
Others on request
Under proper storage conditions the shelf life is 12 months.

Definition
ChEBI: A HEDP that is (ethane-1,1-diyl)bis(phosphonic acid) having a hydroxy substituent at the 1-position. HEDP inhibits the formation, growth, and dissolution of hydroxyapatite crystals by chemisorption to calcium phosphate surfaces.
Manufacturing Process
Phosphorous acid was premixed with acetic acid to form a 50 wt % solution of phosphorous acid dissolved in acetic acid. HEDP were mixed on a molar basis of 1.36:1, acetic acid to phosphorous acid, and this corresponded on a mol percentage basis to 57.6% acetic acid and 42.4% phosphorous acid. Acetic anhydride was continuously metered into a stream of the phosphorous acid-acetic acid mixture to form the reaction solution. The acetic anhydride was metered into the acid mixture at a mol ratio of 1.33 mols of acetic anhydride per mol of phosphorous acid. The metering rates were 18.5 lb/hr of the phosphorous acid/acetic acid premixed solution and 15.1 lb/hr acetic anhydride. The reaction solution was continuously passed through a heat exchanger where it was heated to 190°F then it was continuously fed into a two stage back-mix reaction zone where due to the heat of reaction the temperature rose to 275°F. The average residence in the reaction zone was 27 min. The reaction zone consisted of two back-mix reactors each having a capacity of 7.5 pounds of the reaction solution. A stream of reaction solution was continuously with drawn from the second reactor and continuously mixed with a stream of water which was being metered at a rate of 2 lb/hr. This amount of water corresponded to 18% excess over the theoretical amount necessary to hydrolyze all of the acetyl-containing compounds in the reaction solution to free acids. The hydrolyzed solution was continuously passed through a heat exchanger and cooled to room temperature after which the solution was continuously passed to a crystallizer where, with agitation, the HEDP crystallized. The slurry was then filtered and the crystals were recovered and dried. Analysis of the product showed a conversion rate of phosphorous acid to HEDP of 86%. Sodium hydroxide may be used to give the disodium salt.

1-Hydroxyethane-(1,1-diphosphonic acid) (HEDP ) is extensively used in many technical applications. This work, as a first stage, examines the adsorption of aqueous HEDP, Cu(II), and Zn(II) onto boehmite (gamma-AlOOH) as single solutes. These processes can be described by the formation of inner-sphere complexes by the surface complexation model with constant capacitance. Uncomplexed HEDP is adsorbed as a mononuclear complex over the entre pH range. Four mononuclear surface complexes with different protonation levels are required to obtain a good fit of the experimental data for the pH range studied. Cu(II)- and Zn(II)-HEDP complexes at equimolar concentrations are studied at high and low surface density. The results indicate that the presence of HEDP significantly promotes metal adsorption at low pH in defects of surface sites. However, metal adsorption exhibits the same trend in the absence and presence of HEDP when the surface sites are in excess. The constant capacitance model successfully describes the experimental data through a ligand-like adsorption complex at low pH. At high pH, the model predicts separate adsorption of divalent metal and HEDP onto different surface sites as the preferred adsorption form.