With the gradual depletion of mineral resources, land and human resources of the ocean deepening understanding, the ocean has become a multi-metallic mineral remarkable strategic resource of the 21st century, our country since the 1980s, have been carried out and the rich polymetallic nodules Research on resource exploration, mining, processing and application technologies for cobalt crusts.
The main purpose of developing polymetallic nodules and cobalt-rich crusts in the ocean is to extract valuable metals such as Co, Ni, Cu, etc. The wet extraction process currently under trial will produce solids equivalent to about 35% by weight of the ore. Residue (leaching residue). If these leaching slags cannot be utilized, long-term stacking will cause environmental problems.
The polymetallic nodules and cobalt-rich crust resources in the ocean have not yet been exploited on a large scale. The environmental hazards that may result from smelting and leaching slag are getting more and more attention, but the research on the performance and application of leaching slag is lagging behind.
In this study, the development and utilization of polymetallic nodules and cobalt-rich crust leaching slag in the ocean was carried out. The chemical composition, phase composition and physicochemical properties of the leaching slag were analyzed and tested. It was found that the leaching slag contains a large amount of nano-minerals and has a large The specific surface area and surface activity have good application prospects in the field of environmental protection. The occurrence of rare earth elements is studied. It is believed that light rare earths are mainly adsorbed on the surface of nanoparticles and have potential development value.
First, sample and test
Polymetallic nodules and cobalt-rich crusts were collected from the Pacific International Sea. The powder of polymetallic nodules (86% of particles with a particle size of about 0.074 mm) was extracted by ammonia leaching. The solid residue after Ni, Co and Cu was called ammonia leaching. Slag (code Nod, the same below); cobalt-rich crust powder (77.8% of particle size about 0.074 mm). The solid residue after extracting Ni, Co, Cu, Mn, Zn by acid leaching process is called acid leaching residue. (Code name Cru, the same below).
Ammonia leaching residue and acid leaching slag were analyzed by constant element (wet chemical analysis method), trace amount and rare earth element (neutron activation method). X-ray powder crystal diffraction analysis (DMAX-RC type), differential thermal analysis (LCP-1 type) and mineral size and morphology measurement (Hitachi H8100 transmission electron microscope, TEM); specific surface area (Autosorb-1 type specific surface meter) ), density (U1-1000 true density meter), pH (PHS-3C type acidity meter) and adsorption rate of saturated NaCl water vapor and SO 2 gas.
Second, the results and discussion
(1) Mineral composition and content, the mineral composition of the leaching slag was determined according to X-ray powder diffraction (Fig. 1) and differential thermal analysis (Fig. 2), and their contents were estimated by combining chemical composition. The result was: Nod Zhongling manganese The ore content is about 50%, followed by quartz , kaolinite and feldspar (the total content of the three is about 15%). According to the X-ray diffraction curve 20, the background value of the bottom is increased by about 30. Nod also contains about 35% of amorphous or low crystallinity solids: the content of hemihydrate gypsum in Cru is about 20%. iron ore and silica concentrations are about 10%, jarosite content of less than 5%: an amorphous or low crystallinity of solids content of about 55%. Compared with the original ore, it is found that rhodochrosite, hemihydrate gypsum, jarosite and goethite are new minerals in the wet smelting process. Quartz, kaolinite and feldspar are residual minerals in the ore, and energy spectrum analysis 1) Further confirming the presence of rhodochrosite in Nod and discovering siderite.
Fig.1 X-ray powder crystal diffraction pattern of ammonia leaching residue and acid leaching residue
Fig. 2 Differential thermal analysis of ammonia leaching residue and acid leaching residue
Table 1 Chemical composition of rhodochrosite, siderite and jarosite (%) a)
a) Analysis by energy spectrometer (film sample, no standard) of Hitachi H8100 transmission electron microscope by National Laboratory of Mineral Rock Materials of China University of Geosciences
According to X-ray powder diffraction peaks characteristic calculation unit cell parameters rhodochrosite is: a 0 = b 0 = 0.48nm , c 0 = 1.573nm, γ = 120 °, hexagonal; lattice parameters for the hemihydrate gypsum : a 0 = 1.206 nm, b 0 = 1.272nm, c 0 = 0.692nm, γ = 90.19 °, false orthorhombic, ammonia leaching residue: 114 ℃ removal of H 2 O -, 134 ℃ removal of H 2 O + , 508 ° C rhombohedral decomposition, 798 ° CMn 2 O 3 changed to Mn 3 O 4 ; acid leaching residue: 124 ° C to remove H 2 O - , 174 ° C hemihydrate gypsum dehydration, 416 ° C jarosite dehydration, 634 ~ 656 ° C yellow potassium iron sputum decomposition, 1132 ° C CaSO 4 partial decomposition.
(2) Mineral morphology and particle size. TEM observations show that the Nod Zhongling manganese ore is mostly in the form of fiber bundles (Fig. 3(a)), and the fiber bundle diameter is mostly 15-20 nm and the length is about 100 nm. The hemihydrate gypsum in Cru has two kinds of granular (Fig. 3(b)) and fiber bundle: the former has a particle size of 12-15 nm; the latter has a diameter of about 80 nm and a length of about 400 nm.
Figure 3 TEM photo of rhodochrosite and hemihydrate gypsum
(3) Density and pH. The measured true densities of the Nod and Cru powders (average of 8 measurements) were 3.065 and 2.827 g/cm 3 , respectively . Their pH values ​​in aqueous solution were 8.94 and 3.38, respectively.
(4) Specific surface area and adsorption. The measured specific surface areas of Nod and Cru were 109.56 and 252.8 m 2 /g, respectively. It can be seen from Fig. 4 that the isothermal adsorption-desorption curve of Nod to N 2 intersects only when the relative pressure (P/P 0 ) is lower and higher, and the characteristics are similar to those of the solid without the pore structure. Unlike Nod, the removal of Cru The curve shows a steep change at P/P 0 of about 0.52 and quickly coincides with the adsorption curve (Fig. 4), which is similar to smectite with a 2:1 layered structure. It indicates that there is a mineral with a pore structure in the Cru, but the pore volume of this mineral is small, only 1.23×10 -2 mL/g, and the internal specific surface area generated by the pore structure is only 30 m 2 /g. This is related to the pore structure left by the loss of part of the water molecules in the structural unit layer during gypsum calcination.
Figure 4 Adsorption-desorption curve of ammonia leaching residue and acid leaching residue on N 2
After Nod, Cru and natural pure gypsum powder (particle size of about 0.074 mm accounted for more than 85%) after drying at 550 ° C for 2 hours, the adsorption rate of saturated NaCl water vapor in a constant temperature closed vessel at 30 ° C for 12 hours showed that The particle adsorption capacity is large, the specific surface area is large, the adsorption capacity of the crucible structure is 12.90%; the coarse particle, No microporous structure Nod, the adsorption rate is 10.64%; the coarsest natural gypsum adsorption rate is only 3.00%. The adsorption amounts of the Nod and Cru powders (room temperature, 30 minutes) to the SO 2 gas were 2.47 and 2.25 cm 3 /g, respectively. The strong adsorption capacity of Nod and Cru powders on saturated NaCl aqueous solution vapor and SO 2 is related to the existence of a large number of atomic coordination of nanoparticles and the surface atoms which are easily combined with other atoms and molecules.
From the specific surface area (Sw/m 2 ·g -1 ) and the density (Ï/g·cm -3 ), the average diameter of the particles (d/nm) was calculated according to the formula (d=6×10 3 /Ï·Sw). The particles are spherical): The average particle diameters of Nod and Cru are 17.9 and 9.5 nm, respectively, which are in good agreement with the TEM measurements.
(5) Rare earths - trace elements and chemical components. The rare earth element content of Nod is similar to that of deep sea sedimentary clay (669.5μg/g), but the rare earth element content of Cru is more than twice as high as that of deep sea sedimentary clay (Table 2), especially the light rare earth element content of Cru (1391.6μg/g). The industrial grade (1000μg/g) of weathering shell ion-adsorbed rare earth ore has been reached, and the extraction of rare earth elements in the leaching slag by using MgCl 3 solution with a concentration of 1mol/L (15mL MgCl 3 solution per gram of leaching residue, at room temperature After stirring for 20 minutes and filtering the content of rare earth elements in the supernatant, it was found that the exchangeable ratios of elements such as Sm, Eu, Tb and Yb were all above 80% (Table 3), indicating that they were mainly adsorbed on the surface of the nanoparticles in an ionic state. . In addition, the ∑FeO content of the two samples was higher (Table 4); the P 2 O 5 of Cru was significantly enriched, and the content of harmful elements As and U was higher (Table 5).
Table 2 Rare earth element content (μg/g) of ammonia leaching residue and acid leaching residue a)
a) Institute of High Energy Physics, Chinese Academy of Sciences, using neutron activation method
Table 3 Exchangeable rare earth element content (μg/g) and exchange rate (%) in ammonia leaching residue and acid leaching residue a)
a) China University of Geosciences (Beijing) Inductively Coupled Plasma Mass Spectrometer Laboratory using ICP-HEX-MS mass spectrometer
Table 4 Chemical composition of ammonia leaching residue and acid leaching residue (%) a)
a) China University of Geosciences (Beijing) Chemical Analysis Laboratory uses wet chemical analysis
Table 5 Trace element content of ammonia leach residue and acid leach residue (μg/g) a)
a) Institute of High Energy Physics, Chinese Academy of Sciences, using neutron activation method
(6) Mechanism of nano mineral formation. During the ammonia leaching process, the manganese minerals in the polymetallic nodules (manganese- magnesium- manganese ore, hydromanganese ore, sodium-manganese ore, etc.) undergo a reduction reaction under the action of CO and Cu + , and Mn 4+ is reduced to Mn 2+ , and The CO 3 2- in the solution combines to form MnCO 3 (manganese ore). In the acid leaching process, manganese (iron) minerals, carbonates, etc. in the cobalt-rich crust are decomposed under the action of H 2 SO 4 and SO 2 , and the Ca 2+ and Fe 3+ and K + ions generated are respectively SO 4 2- combines to form CaSO 4 · 2H 2 O (gypsum) and K 2 O·3Fe 2 O 3 · 4SO 4 · 6H 2 O (xanthine). In the above process, CO 3 2- and SO 4 2- in the solution act as a precipitating agent and have positive significance for the formation of nanoparticles.
The formation of nanoparticles occurs synchronously with the decomposition of minerals in the ore, and the whole process is in a short time (ammonia immersion process 90-120 minutes; acid leaching process 30 minutes), lower temperature (ammonia immersion process 50 ° C; acid The immersion process is 30 ° C), the concentration of the precipitant is constantly changing and the dynamic conditions of stirring are carried out, which is beneficial to the formation of a large number of crystal nuclei, but is not beneficial to the rapid growth of the crystal, and is a kinetic factor for controlling the formation of nano-scale minerals.
The gypsum produced during the reaction loses 3/2 crystal water to hemihydrate gypsum when dried at 110 ° C, forming open pores parallel to the (010) plane, and contributes 1.23 × 10 -2 mL / g pore volume and 30 m 2 / g internal specific surface area.
Third, the conclusion
The solid residue (acid leaching residue) after the extraction of Co, Ni, Cu, and the cobalt-rich crust by the ammonia leaching of Co, Ni, Cu, and cobalt-rich crusts by ammonia leaching Containing a large amount of nano-minerals, it has a large specific surface area and surface activity, and has strong adsorption capacity for saturated NaCl water vapor, N 2 , SO 2 and metal cations. It is a nano-adsorbent material with potential application value in environmental protection. The acid leaching residue has a high content of lanthanum FeO, P 2 O 5 and ion-adsorbed rare earth elements, and is expected to be a raw material for nano-functional materials.
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