Quartz could be activated by metal ions dissolved from wolframite surfaces, making it difficult to separate wolframite from quartz. In this study, sodium silicate used as depressant was investigated in the flotation of fine wolframite. Sodium silicate showed the selective depression on the activated quartz, and the flotation separation of fine wolframite could be achieved by depressing quartz. It was revealed that the adsorption of sodium silicate on activated quartz surfaces was more obvious than that on wolframite. Si(OH)₄ and species of aqueous sodium silicate preferentially reacted with activated quartz surfaces and prevented the octyl hydroxamic acid adsorption, further decreasing its floatability.

Efficiently discovering the interaction of the collector oleate and siderite is of great significance for understanding the inherent function of siderite weakening hematite reverse flotation. For this purpose, investigation of the adsorption behavior of oleate on siderite surface was performed by density functional theory (DFT) calculations associating with atomic force microscopy (AFM) imaging. The siderite crystal geometry was computationally optimized via convergence tests. Calculated results of the interaction energy and the Mulliken population verified that the collector oleate adsorbed on siderite surface and the covalent bond was established as a result of electrons transferring from O1 atoms (in oleate molecule) to Fe1 atoms (in siderite lattice). Therefore, valence-electrons’ configurations of Fe1 and O1 changed into 3d^6.514s^0.37 and 2s^1.832p^4.73 from 3d^6.214s^0.31 and 2s^1.83p^4.88 correspondingly. Siderite surfaces with or without oleate functioned were examined with the aid of AFM imaging in PeakForce Tapping mode, and the functioned siderite surface was found to be covered by vesicular membrane matters with the average roughness of 16.4 nm assuring the oleate adsorption. These results contributed to comprehending the interaction of oleate and siderite.

The influence of quartz on the flotation of fine wolframite using octyl hydroxamic acid (OHA) as the collector was investigated by micro-flotation tests, inductively coupled plasma (ICP) measurements, adsorption experiments, zeta potential, and Fourier transform infrared spectroscopy (FT-IR) analysis. Micro-flotation tests showed that a large difference in floatability existed between fine wolframite and quartz in the pH range of 7.0 to 10.0. However, in a synthetic mixture, the flotation separation of fine wolframite from quartz became more difficult as the particle size of the latter decreased. When a dissolved solution of wolframite was used as the flotation medium, quartz floatability improved significantly. Zeta potentials of quartz particles shifted positively in the dissolved solution of wolframite compared to distilled water, especially at a pH level of 7.0–10.0, which was attributed to the metal ions dissolved from the wolframite being adsorbed onto the quartz surface. The surface activation of quartz led to an increase in the OHA adsorption and made the surface hydrophobic. FT-IR analysis further demonstrated that OHA could adsorb onto the activated quartz surface through a dominantly chemical process.

For effective utilization of the residues, calcium sulfate whiskers were prepared from semi-dry desulfurization residues by hydrothermal synthesis reactions. Aiming at collecting the products with a long length and large aspect ratio, the additives, including sodium oleate, sodium dodecyl benzene sulfonate (SDBS), and sodium citrate, were added to control the growth of the crystal. Compared with no additives, whiskers with relatively a longer length and larger aspect ratio could be obtained in the presence of sodium oleate or SDBS. The sodium citrate made the whiskers thicker and shorter. Then, the effects of the additives on crystal growth and the morphology of the hydrothermal products were investigated with the aid of X-ray diffraction (XRD) patterns and molecular dynamics simulations. According to the results of XRD, the diffraction intensity of the crystal face (400) increased under the influence of sodium oleate, promoting crystal growth along the c-axis. The molecular structures of the corresponding faces were built based on the strong peaks shown in the XRD patterns. The atomic distribution on the computed crystal faces was presented. The interaction energies on different faces were calculated to illustrate the different adsorption configurations of the additives. Among the calculated faces, the interaction energies on (400) were both most negative for sodium oleate and SDBS. Therefore, sodium oleate and SDBS preferred to adsorb on (400). As a result, the growth of (400) was thus inhibited and the crystal grew along the c-axis. Compared with sodium oleate and SDBS, the lowest adsorption energy of sodium citrate on the face (310) indicated that sodium citrate has no positive effect on the directional growth of the crystal parallel to c-axis. The molecular simulation results were virtually identical to the crystal faces analysis results.