MgO & P₂O₅ in Phosphate Rock

Application Note EDXRF1587

EDXRF1587

Scope

The measurement of the control oxides P₂O₅ and MgO is demonstrated, as well as other major oxides in phos rock.

Background

Phos rock (phosphate rock, rock phosphate, phosphorite) is mined from high phosphorous clay deposits and processed to be used in fertilizers. During mining and processing it is critical to measure and monitor the levels of P₂O₅ and MgO, as well as the other major oxides CaO, Al₂O₃, SiO₂, and Fe₂O₃ to ensure proper product quality of the physical and chemical properties desired. To meet this industry need, Rigaku offers NEX QC+ EDXRF analyzer. The self-contained unit with touchscreen operation is ideal for at-line quality checks by non-technical operators, as well as in the QA/QC lab.

NEX QC+ high-resolution EDXRF analyzer

Model: NEX QC+

Calibration

For demonstration, an empirical calibration was built using a set of seven commercially available standards. Two of the calibration standards are certified reference materials. Boric acid was measured to generate special background correction that automatically compensates for the specific amount of background in each individual sample measured.

Control Oxides

P₂O₅
Units: mass %
Sample I.D. Standard value Calculated value
SARM 32 39.96 39.945
CRM CGL 107 26.38 26.144
GPO-01 28.66 28.967
GPO-17 13.55 13.387
GPO-15 25.22 25.302
GPO-16 17.76 18.206
GPO-14 24.52 24.099

EDXRF1587 Correlation plot P2O5Correlation plot P₂O₅


MgO
Units: mass %
Sample I.D. Standard value Calculated value
SARM 32 0.50 0.501
CRM CGL 107 2.26 2.257
GPO-01 0.83 0.830
GPO-17 5.82 5.825
GPO-15 2.90 2.933
GPO-16 6.38 6.377
GPO-14 3.07 3.034

EDXRF1587 Correlation plot MgOCorrelation plot MgO

Other oxides

Oxide Concentration range
CaO 39 – 55%
Fe₂O₃ 0.1 – 3.5%
Al₂O₃ 0.05 – 1.8%
SiO₂ 0.4 – 21%

Repeatability

To demonstrate repeatability (precision), the low and high calibration standards were chosen. Each sample was measured in static position for ten repeat analyses with typical results shown below.

Sample: SARM 32
Units: mass %

Oxide

Standard value

Average value

Std. dev

% Relative

P₂O₅

39.96

40.066

0.070

0.2

MgO

0.50

0.505

0.012

2.4

CaO

54.44

54.361

0.040

0.1

Fe₂O₃

0.14

0.141

0.003

2.1

Al₂O₃

0.05

0.059

0.008

16

SiO₂

0.40

0.470

0.022

5.5


Sample: GPO-17
Units: mass %

Oxide

Standard value

Average value

Std. dev

% Relative

P₂O₅

13.55

13.479

0.027

0.2

MgO

5.82

5.910

0.066

1.1

CaO

39.14

38.812

0.079

0.2

Fe₂O₃

1.29

1.277

0.005

0.4

Al₂O₃

1.83

1.890

0.018

1.0

SiO₂

11.62

11.777

0.126

1.1

Conclusion

The performance shown here demonstrates NEX QC+ provides excellent sensitivity and performance for the measurement of P₂O₅, MgO and other major oxides in phos rock. Self-contained with simple touch screen operation, NEX QC+ is an excellent tool for at- line control and quality checks throughout the mining and processing of phos rock. 

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