Determination of Calcium Content in Manganese Ore Using Wayeal Atomic Absorption Spectrophotometer

In manganese dioxide ore, calcium is primarily present in the form of compounds such as calcium carbonate and calcium silicate. During high-temperature smelting, these compounds tend to generate slag with a high melting point, thereby increasing the viscosity of the molten mass and impeding the reduction and separation of manganese. Determination of calcium content enables the prediction of slag volume and slag system characteristics, thereby facilitating adjustments to the coke charge ratio or the addition of acidic flux (e.g., quartz sand). Consequently, this improves melt fluidity, enhances metal recovery efficiency, and lowers energy consumption.

High levels of calcium impurities adversely impact the quality of manganese dioxide ore. Particularly in the production of battery-grade manganese products, the calcium content is subject to extremely stringent control (generally required to be less than 0.1%). The detection of calcium helps determine whether pretreatment methods such as ore washing, flotation, or chemical leaching are needed to remove calcareous gangue, thereby ensuring the quality of subsequent products. Certain sedimentary or hydrothermal manganese dioxide ores often coexist with calcareous minerals. If the calcium content is high but the deposit is of a certain scale, it may be considered for synergistic development as steelmaking flux or cement raw material. The analytical results provide data support for the graded utilization of the ore and the extension of the industrial chain, thereby enhancing the overall economic value.

Keywords: Atomic absorption, Flame method, Manganese dioxide, Calcium.

1. Experiment Method

1.1 Instrument Configuration

Table 1 Configuration List of Atomic Absorption Spectrophotometer

1.2 Reagents and Experiment Material

1.2.1 Calcium standard solution: 1000mg/L

1.2.2 Hydrochloric acid: Guaranteed reagent (GR)

1.2.3 Hydrogen peroxide: Guaranteed reagent (GR)

1.2.4 0.2% Lanthanum chloride solution: Weigh 0.2g of anhydrous lanthanum chloride, dissolve in ultrapure water, and dilute to 100mL in a volumetric flask.

1.2.5 Polytetrafluoroethylene (PTFE) crucible

1.2.6 Analytical balance (0.0001g readability / 1/10000 precision)

1.2.7 Ultrasonic cleaner

1.2.8 Digital electric hot plate

1.3 Sample Pretreatment

Accurately weigh 0.1g (to the nearest 0.0002g) of the sample into a 50mL PTFE crucible. Add 10mL of (1:1) hydrochloric acid and swirl to mix. Then add 5mL of hydrogen peroxide (first add dropwise, and after the reaction is complete, add the remaining reagent in one portion), and swirl again. Heat on a hot plate at 250 °C to evaporate the acid until the content is reduced to approximately the size of a soybean. Remove and allow to cool slightly, then rinse the inner wall of the crucible with 0.2% lanthanum chloride aqueous solution. Transfer the solution to a 50mL volumetric flask, dilute to the mark with 0.2% lanthanum chloride aqueous solution, and mix well for subsequent measurement. A sample blank should be prepared simultaneously using the same procedure.

2. Result and Discussion

2.1 Spectral Conditions for the Element

2.1.1 Standard Curve Test

Calibration Curve Linearity for Calcium Element:

2.1.2 Sample Test

A Sample Chromatogram

3. Attention

1. During sample pretreatment, the hydrogen peroxide solution added is a strong oxidizing agent and should only be added dropwise into the crucible. Allow each drop to react completely before adding the next drop. After the entire reaction is complete, add the remaining hydrogen peroxide solution. This entire process must be carried out inside a fume hood. Ensure proper experimental protection.

2. Both the calibration curve standards and the samples are diluted to volume with 0.2% lanthanum chloride aqueous solution. In the determination of calcium by flame atomic absorption spectrometry, lanthanum solution is used to eliminate chemical interferences and to act as a releasing agent for calcium.

4. Conclusion

From the experimental results, the linear correlation coefficients for calcium were all greater than 0.999, and the RSD of three replicate injections was less than 0.2%. This method is accurate, reliable, and highly sensitive, and can be used for the determination of calcium in manganese dioxide ore.