Chromium (III) hydroxide

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption

Remarks:

other: extractability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1980

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented publication which meets basic scientific principles

Data source

Reference

Reference Type:

publication

Title:

Extractable Chromium as Related to Soll pH and Applied Chromium

Author:

Grove, J.H. und Ellis B.G.

Year:

1980

Bibliographic source:

Soil Science Society of America Journal 44, 1980, 238 - 242

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

extractability in different solvents depending on time

GLP compliance:

not specified

Type of method:

other: batch extractability depending on time

Media:

soil

Test material

Test material information

Constituent 1

Reference substance name:

Chromium trichloride

EC Number:

233-038-3

EC Name:

Chromium trichloride

Cas Number:

10025-73-7

Constituent 2

Reference substance name:

Chromium(III) chloride

IUPAC Name:

Chromium(III) chloride

Test material form:

other: solution in water

Study design

Test temperature:

25°C

Batch equilibrium or other method

Analytical monitoring:

yes

Details on sampling:

sampling first at 24 hours and then at 1 ,2, 4, 8 and 16 weeks

Details on matrix:

COLLECTION AND STORAGE
- Geographic location:
Rubikon sand from Muskegon County, Michigan
Morley clay loam from Ionia County, Michigan
Morley clay loam, limed, from Ionia County, Michigan (liming: adjustion to pH 7.5 with Ca(OH)2)
- Sampling depth (cm):top 5 and 10 cm
- Soil preparation: The soil was passed through a 2 mm plastic sieve, air-dried, and divided into 1•kg portions.

PROPERTIES
- Horizon:
Rubicon Sand: A
Morley clay loam: Ap
- Soil taxonomic classification:
Rubicon sand: sandy, mixed frigid Entic Haplorthod
Morley clay loam: fine, illitic, mesic Typic Hapludalf
- pH:
Rubikon sand: pH 4.7
Morley clay loam: pH 5.4
Morley clay loam, limed: pH 7.5
- Organic carbon (%):
Rubikon sand: 2.2
Morley clay loam: 4.2
Morley clay loam, limed: 4.2
Natural Chromium content (average of 12 replications):
Rubicon sand: <0.1 ppm (detection limit)
Morley loam: 16.0 ppm

Details on test conditions:

TEST SYSTEM
Three replications of 0 and 500 ppm Cr as Cr(III) were applied 10 all three soils in the initial wetting water.
The moisture contents for the Rubicon and Morley soils corresponds were 14 and 29%, respectively. All pots were thorougbly mixed, covered with polyethylene to minimize water vapor loss, and placed in a constant temperature (25°C) chamber. Pots were sampled at 24 hours, 1, 2, 4, 8. and 16 weeks, All samples (5 g) were extracted on an end-over-end shaker in succession with the extractants. Separation of liquid and solid phases was made by centrifugation with the solid being retained for subsequent extraction. The citrate-dithionite- bicarbonate extraction is that of Mehra and Jackson (1960). The extractants were selected to remove water•soluble, exchangeable, organic-bound, amorphous-precipitated, and more crystalline.precipitated Cr. After each extraction the samples were centrifuged at 27 000 g for 15 min and decanted.

Results and discussion

Results: Batch equilibrium or other method

Statistics:

In the analysis of variance for extractable Cr, the resulting split-plot design (extractant within incubation time within level of a Cr source within a soil) all main effects and all interaction terms gave highly significant F values.
In the analysis of variance for soil pH a similar split-plot design (incubation time within level of a Cr source within a soil) also gave highly significant F values for aIl main effects and all interaction effects.

Any other information on results incl. tables

Ammonium chloride and Cupric sulfate extractable fractions were generally negligible.

This means, that there is no exchangeable or organic bound Cr(III) present in the soils.

80 to 99% of all extractable Cr being present in the water, oxalate, and the dithionite-citrate extractions. Early extrations (24 hours and 1 week) with NH₄Cl and CuSO₄resulted in appreciable quantities, but declined to near zero values after 2 weeks.

Chromium converts rapidly to the oxalate and dithionite-citrate extractable fractions, the latter fraction was the largest.

The water-soluble fraction declined in importance in all soils with time.

Chromium(III) addition reduced soil pH in all soils with the greatest decrease in Rubicon soil.

Addition of CrCl₃solution to the soils results in formation of insoluble Cr(OH)₃and subsequent ageing of the precipitate, resulting in lowering the water soluble fraction after one week. Reduction of the pH by consumption of H+ enhances the formation of insoluble Cr(OH)₃.

Organic bound Cr appears to be negligible. The effectiveness of CuSO₄as an extractant may be questionable, but ist is concluded by the authors that the data from this study give strong evidence that organic Cr(III) complexes are very low in quantity in these soils.

Deduced from the Figures of the publication, in Rubicon sand, the initial water soluble Cr(III) was ca. 29%, decreasing to ca. 3% after 2 weeks and being nearly zero after 16 weeks. Whereas the citrate-dithionite soluble fraction representing the precipitated and aged Cr(OH)₃results of ca. 19% after 24 hours, ca. 63% after 2 weeks, and ca. 75% after 16 weeks.

In Morley clay loam and limed Morley clay loam the water extractable fraction is ca. 1.5% in both soils and nearly zero after 2 and 16 weeks, respectively.

The citrate-dithionite soluble fraction representing the precipitated and aged Cr(OH)3 is in Morley clay loam and limed Morley clay loam after 24 hours 47 in both soils, after 2 weeks 47 and 48%, repectively and after 16 weeks 83 and 68% respechtively.

It should be taken in account that these values are not precise, because they have been derived from diagrams from the publication. However it can be concluded that Chromium(III) is precipitated in soils to form insoluble Chromium(III)hydroxide. Chromium(III)hydroxide formation consumes H+ and therefore Cr(III)hydroxide formation in forced resulting in reduced pH of the soils. After 2 weeks the water soluble fraction is negligible. Most added Cr(III)chloride is present in precipitated water insoluble form.

Applicant's summary and conclusion

Validity criteria fulfilled:

not applicable

Conclusions:

Chromium(III)hydroxide is formed in soils at pH >4.7. Formation of Chromium(III)hydroxide is forced, as the reaction consumes H+ and reduces pH of soils. In soils precipitated Chromium(III)hydroxide is aged with time resulting in more crystalline forms with lowered solubility. There is strong evidence that organic bound Chromium(III) is very low. The exchangeable portion of Cr(III) is also negligible.

Executive summary:

Chromium(III)chloride was added to three soils (Rubikon sand, Morley clay loam and limed Morley clay loam) resulting in 500 ppm Cr(III). After 24 hours and then at 1 ,2, 4, 8 and 16 weeks, the soil samples (5g) were extracted withdeionized-distilled water, 1 m NH4Cl, 1 m CuSO4, 0.3 m Ammonium oxalate and Sodium citrate/sodium dithionite/sodium bicarbonate repesenring the water-soluble, exchangeable, organic-bound, amorphous precipitated, and the more crystalline-precipitated fraction of Cr(III).

Results:Chromium(III)hydroxide is formed in soils at pH >4.7. Formation of Chromium(III)hydroxide is forced, as the reaction consumes H⁺and reduces pH of soils. In soils precipitated Chromium(III)hydroxide is aged with time resulting in more crystalline forms with lowered solubility. There is strong evidence that organic bound Chromium(III) is very low. The exchangeable portion of Cr(III) is also negligible. The water soluble fraction is nearly zero after 2 weeks.