In the copper ore smelting process, metal ions such as As, Cu, Zn, Ni, and Pb in the solution are usually precipitated by the sulfidation method, that is, sodium hydrogen sulfide, sodium sulfide or hydrogen sulfide gas is added to make the metal ions form sulfide Form precipitation, resulting in a large amount of sulfide slag. Sulfide slag contains a large amount of valuable metals such as Cu, Zn, Ni, Pb, etc., which has great recovery value.
During the treatment of sulfide slag, it is necessary to detect the content of metal elements. Currently commonly used methods are AAS, ICP-MS, ICP-OES and so on. Among them: the AAS method has strong anti-interference ability, but the atomization efficiency is low; the ICP-OES method has good sensitivity and strong salt resistance ability, and can measure the number of multispectral lines, but cannot determine isotopes; The ICP-MS method has low detection limit, high precision, can detect trace elements, and can analyze element content by determining isotope with less interference.
During the detection process, solid samples need to be digested. Digestion methods include electric hot plate heating method, graphite method, high pressure sealing method, microwave method, etc. When the ICP-MS method is used for the determination, the digestion method of the sample has a certain influence on the determination result. The microwave digestion method has a high recovery rate and can quickly determine a variety of heavy metal elements, but the sampling volume should not be too large, and the digestion of refractory substances in biological samples is not complete; graphite digestion takes a long time to digest certain samples, and some substances cannot be completely digested. The equipment requirements are high and the maintenance cost is high; the heating plate digestion time is long, the acid consumption is large, and the non-closed digestion is easy to cause harm to the human body and the environment. The high-pressure closed digestion method is carried out in a closed digestion tank, which can prevent external pollution, avoid waste gas and waste acid discharge, is easy to operate, and can handle complex samples. Therefore, the sample is completely digested, and the measurement results are of high precision and accuracy. . The test adopts the high-temperature closed digestion method to digest the sulfide slag, and then uses the ICP-MS method to measure Cu, Zn, Ni, and Pb in it, in order to provide a suitable measurement method for the enterprise to deal with the sulfide slag.
1 Experimental part
1.1 Materials and reagents
Nitric acid (HNO3, 14.40 mol/L), hydrochloric acid (HCl, BWG083800-500, 1.001 mol/L), hydrofluoric acid (HF, BWR3023-2016, 0.050 17 mol/L), ultrapure water (resistivity ≥ 18.2 MΩ cm), standard solution containing 33 elements such as Cu, Zn, Ni, Pb (GNM-M330198-2013, 100 mL, 100 μg/mL, matrix is 5% HNO3, HCl or HF), yttrium (Y) standard Solution (GSB04-1788-2004, 50 mL, 1000 μg/mL, matrix is 1 mol/L HNO3), iridium (Ir) standard solution (GSB04-17322004, 50 mL, 1000 μg/mL, matrix is 2.0 mol/L L HCl solution).
Sulfide slag: It was taken from the arsenic removal process of the electrowinning waste liquid treatment plant of a copper smelter in Guangxi.
Copper, zinc, nickel, lead standard ores, national standard material resource sharing platform.
Mixed acid: 2 mL HNO3+1 mL HCl+1 mL HF.
Standard curve: take the element standard solution, use the quality control method to make the ratio, and dilute it with 0.288 mol/L HNO3 solution to the mass concentration of 0.5, 1, 5, 10, 50, 100, 500 μg/L, and then in the instrument Determine and draw the standard curve of the analyte under the optimal conditions.
1.2 Instruments and equipment
Sartorius precision balance (GL2202-1SCN, Germany Sartorius company), Prand Micro Transferpette S adjustable pipette gun (Germany BRAND company), DZF-6012 electric blast drying oven (Shanghai Zhongben Technology Co., Ltd.) , GCXJ-25 high-pressure closed digestion tank (Shanghai Xinnuo Instrument Group Co., Ltd.), Milli-Q ultrapure water instrument (Millipore Corporation, USA), and Agilent 7800X inductively coupled plasma mass spectrometer (Agilent Corporation, USA).
1.3 ICP-MS measurement conditions
The transmission power was 1350 W, the pump speed of the peristaltic pump was 60 r/min, the atomization gas flow rate was 8 L/min, the cooling argon flow rate was 13 L/min (argon purity ≥ 99.9%), the retention time was 150 ms, and repeated 3 times. The plasma gas flow rate is 13 L/min.
1.4 Test principle and method
1.4.1 Test principle
During the high-pressure closed digestion process, a high-temperature, high-pressure and strong acid environment will be formed in the tank, which will completely decompose most insoluble elements and ensure that volatile elements will not be lost, and the acid will not volatilize due to high digestion temperature to form an internal cycle.
Sample treatment: The sample contains sulfide, dried and ground, then sealed and digested under acidic conditions, and all the metal ions in it were transferred into the solution. High-pressure closed digestion can also convert target elements in different valence states in solid samples into easily decomposed inorganic compounds to prevent endogenous interference. In the sample, Cu, Zn, Ni and Pb are all divalent elements to be measured. In the mixed acid system: nitric acid can dissolve various sulfides; hydrochloric acid can dissolve various silicates and sulfates under high temperature and high pressure; the combination of hydrofluoric acid, nitric acid and hydrochloric acid can effectively prevent the target elements from forming silicates and affecting the measurement results.
Sulfide slag is a mixed solid substance containing a large amount of heavy metal elements, including S, Cu, Zn, Ni, Pb, As, Bi, Sb, Sn and other elements. Among them: S exists in the form of simple substance, Cu mainly exists in the form of CuS and CuSO4, Zn exists in the form of ZnS, Pb mainly exists in the form of PbS, and Ni mainly exists in the form of NiS.
Measuring principle of the instrument: ICP generates a high-power radio frequency signal through an inductance coil to form a high-temperature plasma inside the coil. The sample forms an aerosol through the nebulizer and is brought into the central area of the plasma torch by high-purity argon to evaporate, decompose and ionize the sample. . The ICP-MS interface transmits the ions in the plasma to the mass spectrometer, and the mass spectrometer selects ions with different mass-to-nucleus ratios to detect the ion intensity and calculate the intensity of a certain element.
1.4.2 Test method
The sulfide slag was dried in a constant temperature oven to a constant weight and ground. The high-pressure closed digestion tank was soaked and cleaned with 1.152 mol/L HNO3 solution and dried in a constant temperature drying oven. Weigh 0.5 g of sulfide slag, add mixed acids in different proportions, place in a high-pressure closed digestion tank, and digest at a constant temperature of 120 °C for 4 to 5 h. After cooling to near room temperature, take it out and heat it on a heating plate. Add 2 mL of ultrapure water 8 times to discharge the acid until the solution is clear without precipitation or suspended matter, then take it out and cool it to room temperature, and dilute to 10 mL with 0.288 mol/L HNO3 for testing.
Take 2 mL HNO3 (14.4 mol/L), 1 mL HCl (1.001 mol/L), and 1 mL HF (0.050 17 mol/L) into a high-pressure closed digestion tank and mix well as a blank reagent.
2 Test results and discussion
2.1 Digestion of samples
Four groups of mixed acids with different proportions were used to digest and measure the sulfide slag according to the test method. The digestion effect of the 2 mL HNO3+2 mL HCl+1 mL HF system was better, and the solution was clear without precipitation. The concentration of nitric acid used in sample digestion was 14.4 mol/L.
2.2 Calculation of detection limit
The detection limit is calculated by the formula L=3s0/k (s0 is the standard deviation value of the blank multiple calculations, k is the slope of the standard curve, and 3 is the coefficient taken under the 99% confidence probability). Continuously measure the blank sample 8 times and fit the measured data.
2.3 Selection of isotopes
Mass spectrum interference will occur during ICP-MS determination. Generally, it is eliminated by mass number selection, plasma shielding and other methods.
The choice of isotope is to overcome the interference of mass spectrum. In principle, it is necessary to select the isotope with large abundance value and low interference. The test determined a sample in advance, and after analyzing the ICP-MS measurement results, it was determined that 65Cu, 66Zn, 60Ni, and 208Pb were the analytical isotopes of Cu, Zn, Ni, and Pb, and the most probable interference element combination that might be caused by the optimal conditions of the equipment was studied.
2.4 Selection of internal standard elements
The internal standard is used to calibrate the transformation of the response signal, and these transformations include matrix effects and instrument drift. The formation of matrix effect mainly comes from non-mass spectrum interference, including atomization effect, ionization effect and charge effect. The matrix effect will cause the stability and precision of the signal to fluctuate. The method to prevent the influence of the matrix effect is the internal standard method, that is, the internal standard substance is added during the pre-measurement treatment to reduce the loss of the components to be measured during the sample processing. The internal standard elements used were determined by pre-determining one sample, and Y and Ir were determined as internal standard elements according to the principle of mass number proximity. Cu, Zn, and Ni were calibrated with 91Y, and Pb was calibrated with Ir, and Y and Ir element standard solutions were used as internal standard solutions with a mass concentration of 10 μg/L.
2.5 Precision of the method
The sulfide slag samples were measured 8 times in parallel according to the test method, and the RSDs of the measurement results were all between 0.83% and 4.69%, indicating that the method has high precision and good repeatability.
2.6 Spike Recovery
In order to verify the accuracy and reliability of the method, the sulfide slag was spiked and recovered in parallel according to the test procedures, and two samples of 0.5 g each were taken to be tested, respectively, and were directly measured by ICP-MS after airtight digestion under high pressure. After adding an appropriate amount of standard substances, it was determined by ICP-MS. The recovery rate of the standard addition was between 97.75% and 100.64%. The recovery rate was relatively high, indicating that the method had high precision and reliability.
2.7 Comparative test of standard ore
According to the test method and procedure, the standard ore is measured, and the standard value is compared with the measured value to verify the accuracy of the method. The error between the standard value and the measured value of the four target elements of the standard ore is within the range of 0.001 to 0.02 g/kg , which is more accurate.
3 Conclusion
High-pressure closed digestion-inductively coupled plasma mass spectrometry was used to determine Cu, Zn, Ni, and Pb in sulfide slag, with good accuracy and reliability, and the recovery rate of the method was between 97.75% and 100.64%. In comparison, the determination errors were all less than or equal to 0.02 g/kg.
The sulfide slag is digested with a certain amount of HNO3+HCl+HF mixed acid solution, the solution is clear without precipitation and suspension, and the digestion effect is good. The method has the advantages of low detection limit, high precision, fast speed, accuracy and reliability, and can be used for the determination of valuable metals in sulfide slag.