Molybdate Test Kits

Visual Kits

Range	MDL	Method	Type	Test Kit	Refill
0 - 7 ppm as Mo	0.5 ppm	Catechol	CHEMets	K-6701	R-6702
2 - 24 ppm as Mo	2 ppm	Catechol	CHEMets	K-6702	R-6702
20 - 200 ppm as Mo	20 ppm	Catechol	CHEMets	K-6720	R-6720

Photometric Kit

Range	Method	Type	Test Kit
0 - 25.0 ppm as Mo	Catechol	Vacu-vials	K-6703

CHEMetrics visual molybdate water treatment test kits employ the well-known Catechol reagent to deliver sensitivity and accuracy within two minutes or less. Suitable for industrial water treatment, power generation and cooling water system testing. Based on CHEMetrics patented Self-Filling Reagent Ampoule technology. Premixed. Premeasured. Precise. Each kit contains 30 tests.

CHEMetrics visual molybdate water treatment test kits feature CHEMets® self-filling ampoules that contain pre-measured reagent for a single test. Simply snap the ampoule directly in a sample to draw in the correct volume of sample and then compare to the supplied colour standards to find the concentration.

CHEMetrics also offers an instrumental molybdate test kit featuring Vacu-vials® self-filling ampoule technology and rely on CHEMetrics direct-readout photometers or spectrophotometers capable of accepting a 13-mm diameter round cell.

Catechol Method

The molybdate test method employs the catechol chemistry. In a mildly reducing alkaline solution, catechol reacts with hexavalent molybdenum to form a yellow-orange coloured chelate in direct proportion to the hexavalent molybdenum concentration. Test results are expressed in ppm (mg/l) molybdenum (Mo).

References:
G. P. Haight and V. Paragamian, Analytical Chemistry, pp. 32, 642 (1960).
H. Onishi and E. B. Sandell, Photometric Determination of Trace Metals, 4^th ed., Part 1, p. 295 (1978).

Technical Data Sheet

Applications

Sodium molybdate salt (Na₂MoO₄) is frequently used throughout the industrial water treatment and power generation industries as an anodic oxidising corrosion inhibitor in both open-loop and particularly in closed-loop, high temperature cooling water systems. In solution, molybdate anions complex with oxidised iron to form a protective film of molybdate and ferric oxide that prevents corrosion of metal components.

Sodium molybdate is considered an effective, environmentally acceptable alternative to chromate treatment as it exhibits low or even negligible toxicity, unlike many other transition elements. Sodium molybdate is also favoured in situations where phosphate or zinc discharges are restricted.

Sodium molybdate is typically used in conjunction with other complimentary corrosion inhibitors as when used alone it requires high concentrations to function effectively. Molybdate also appears to play a role as a biocide against microbiologically induced corrosion (MIC).

Since molybdate is a corrosion inhibitor, testing is critical to prevent damage to your system and control chemical costs. By testing the molybdate concentrations, you can ensure that the system is being dosed with enough corrosion inhibitor to prevent corrosion, such as pitting. Monitoring will also reveal when molybdate concentrations are too high so that operators can take preventative action to stop expensive chemical from being wasted. If your system relies on a molybdate-based corrosion inhibitor, testing is a great way to keep costs low and prevent costly maintenance in the future.

Molybdate has other industrial uses, including the petroleum industry as a precursor to catalysts for the removal of sulphur from petroleum, in anodes and cathodes in aqueous capacitors, in medicine, as a fertiliser additive and as pigments.

What is Molybdate?

Molybdenum (Mo) is a transitional metal in group 6 of the periodic table, below Chromium (Cr). It is a refractory, silver-grey metal with a very high melting point of 2623°C. Iron has a MP of 1538°C. Molybdenum does not oxidise in air below 300°C. Mo reacts readily with halogens, hydrogen peroxide and nitric acid. Molybdenum forms hard, stable carbides and the majority of world Molybdenum production is used for 316 stainless steel production to improve anti-pitting corrosion resistance to acids. Molybdenum is not found in elemental form in the natural environment, but only in its oxidised forms as metallic ores. Molybdenum ores were historically confused with lead ores. Molydenum oxidation states range from -2 to +6.

Molybdate always contains hexavalent molybdenum, in oxidation state +6. There are a large number of different molybdate oxyanions, either discrete or polymeric in structure, the simplest and smallest of which are MoO₄^2- (molybdate) and Mo₂O₇^2- (dimolybdate). The largest contain up to 154 Molybdenum atoms and exist as solids only. Molybdates tend to be readily soluble in water, such as NaMoO₄ and NH₄₄, in contrast to most other molybdenum compounds which have low solubility.