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The Chukchi Sea is the inflow shelf between the Arctic and the Pacific. A comprehensive research on algal dynamics, physical–biological interactions, and impacts on nutrient drawdown was conducted in summer 2010. The study found a phytoplankton bloom with chlorophyll a (Chla) > 10 mg m−3 at ice edge in July. There were 36 shared algal species in both sea ice and open water, and those species dominated numerically both environments highlighting the seeding role of ice algae for the phytoplankton bloom. The succession pattern of diatom genera at three phases from sea-ice to open-water bloom and post-bloom conditions was revealed, and the phytoplankton abundance was positively correlated with the concentration of > 20 µm fractionated Chla. An anticyclonic eddy was detected in July and significantly reduced nutrient inventories in the impacted area relative to historical values. Phytoplankton composition was an important factor for both variable drawdown ratios of silicate to dissolved inorganic nitrogen (1.31–3.37) and dissolved inorganic nitrogen to dissolved inorganic phosphorus (7.62–12.32); however, both ratios also changed between July and August. The results indicated highly dynamic biogeochemical processes during the summer. In addition, the lower bound of silicate drawdown was comparable to the amount imported through the Bering Strait, indicating the Chukchi Sea is a significant silicate sink.

In current COD measurement method, we found that sodium chlorate (NaClO3) can effectively reduce the chemical oxygen demand (COD) of minerals processing wastewater (MPW). However, the reduction in COD via the present COD method was only achieved through the interference of NaClO3 with COD measurement. A series of laboratory-scale experiments demonstrated that the COD reduction is independent of NaClO3 reaction time, reaction pH and reaction temperature, but only related to NaClO3 dosage, and a higher NaClO3 dosage leads to a lower COD. Results further showed that the addition of NaClO3 didn’t affect the initial concentration of the total organic carbon, chloride ions and the benzohydroxamic acid (BHA); their concentration remained unchanged after the addition of NaClO3. Moreover, the residual concentration of NaClO3 also remained same as the initial value. However, COD in both MPW and BHA solution decreased. Furthermore, when added reducing agent to consume the residual NaClO3 before COD measurement, and then the COD was determined to return to its initial value. All these observations clearly shown that NaClO3 doesn’t react with the reducing substances in wastewater under the experimental conditions; it only reacts with reducing substances under the COD measurement conditions. From all these evidences, we concluded that NaClO3 can interfere with the determination of COD. In fact, the interference of NaClO3 is not specified in the standard method, which is a defect of the present COD measurement method. Residual NaClO3 remains in wastewater may cause secondary pollution to the environment. This study, therefore, suggest the government revise and improve the COD measurement method in order to avoid the interference of NaClO3 and prevent the industrial use of NaClO3 for COD reduction of wastewater.

In this study, the horizontal and vertical distribution of primary production (PP) and its monthly variations were described based on field data collected from the Daya Bay in January–December of 2016. The relationships between PP and environmental factors were analyzed using a general additive model (GAM). Significant seasonal differences were observed in the horizontal distribution of PP, while vertical distribution showed a relatively consistent unimodal pattern. The monthly average PP (calculated by carbon) ranged from 48.03 to 390.56 mg/(m2·h), with an annual average of 182.77 mg/(m2·h). The highest PP was observed in May and the lowest in November. Additionally, the overall trend in PP was spring>summer>winter>autumn, and spring PP was approximately three times that of autumn PP. GAM analysis revealed that temperature, bottom salinity, phytoplankton, and photosynthetically active radiation (PAR) had no significant relationships with PP, while longitude, depth, surface salinity, chlorophyll a (Chl a) and transparency were significantly correlated with PP. Overall, the results presented herein indicate that monsoonal changes and terrestrial and offshore water systems have crucial effects on environmental factors that are associated with PP changes.

This study investigates the effects of silicate removal from recycled wastewater on scheelite flotation performance. Systematic experiments were conducted to identify and evaluate the mechanisms underlying the influence of sodium silicate on scheelite flotation and silicate removal. When the sodium silicate concentration exceeds 1 × 10−2 mol/L, scheelite recoveries decrease from 80% to 20% because excess sodium silicate strongly competes with sodium oleate for adsorption sites on the scheelite surface. Under treatment with 5 g/L calcium chloride, silicate removal can reach 90%, and system pH decreases from 12.5 to 11. The reduction of system pH to the range of 11–9 is conducive to promote silicate polymerization and improve silicate removal. The micromorphology and crystal structure of the precipitates that formed under different reaction pH levels were analyzed through scanning electron microscopy coupled with energy dispersive spectrometry, X-ray diffraction, and Fourier transform infrared. The results of these analytical tests confirm that calcium chloride removes silicate through the formation of amorphous calcium silicate hydrate precipitates with low crystallinity. Continuous pilot-scale tests on recycled wastewater treatment and reuse further demonstrate the feasibility and stability of silicate removal. Silicate removal can reach 90%, and system pH can decrease from 11 to 9.5. The use of treated water increases scheelite roughing grade from 0.47% to 0.63% and improves scheelite recovery by 5%.

Silicate removal from scheelite flotation wastewater by flue gas desulphurisation waste (FGD gypsum) has been investigated. Systematic laboratory-scale experiments were conducted to evaluate silicate removal and formation mechanism of calcium silicate. Precipitation test results showed that silicate removal reached 90% at an initial silicon concentration of 2650 mg/L when the dose of FGD gypsum exceeded 20 g/L. Equilibrium speciation analysis showed that solution pH is the key factor affecting silicate removal. Silicate removal could be effectively improved to 95% when pH was reduced to 10. Kinetic analysis showed that reaction rate peaked in 60 s and attained equilibrium after 240 s. Scanning electronic microscopy coupled with energy dispersive spectroscopy (SEM-EDS) results confirmed the formation of calcium silicate and described its morphology features. The continuous pilot-scale test (100 mL/min) further demonstrated the feasibility of utilizing FGD gypsum for silicate removal. Similar results were observed in laboratory-scale experiments. Treatment cost totalled 0.18 $/m3.

This research demonstrates an effective application of etidronic acid to improve the scheelite flotation efficiency and reduce the consumptions of energy and reagents. The cleaning recovery is significantly increased by 7%, and the cleaning cost is reduced by 17% accompanied with the efficient improvement of roughing grade from 1.22% to 1.68% compared with that in previous month. The depression abilities of etidronic acid, normal water glass, and acidified water glass for the scheelite roughing flotation are studied using laboratory-scale experiments. Etidronic acid shows an improved selective performance in improving the roughing grade. This performance is further verified by industrial test. The use of etidronic acid in the roughing circuit improves the product grade from 24.66% to 28.26%. The daily product output is also increases by 1.54 t. Economic evaluation results indicate that the heating cost is reduced by 28%, and the water glass consumption is decreased by 14%. An increased product profit of $1,248,000 and a reduced cost of $20,841 are also obtained.

The size-fractionated biomass and primary production of phytoplankton, and the influence of environmental factors on it were studied in the Dongsha natural gas hydrate zone of the northern South China Sea in May 2013. Low nutrient, low chlorophyll a (Chl a) and primary productivity characteristics were found in these waters. The phenomena of subsurface Chl a maximum layers (SCMLs) and primary production maximum layers (SPMLs) were observed in the Dongsha waters. There were significant differences in the size-fractionated biomass and primary production that showed picophytoplankton>nanophytoplankton>microphytoplankton in terms of biomass and degree of contribution to production. Vertical biomass distribution indicated there were considerable differences among different phytoplankton within the euphotic zone (Zeu) in spring. For example, microphytoplankton was distributed evenly in the euphotic layer and nanophytoplankton was mainly distributed in the subsurface or in the middle of the euphotic layer, while picophytoplankton was mainly distributed in the middle or bottom of the euphotic layer. Smaller cell size and larger relative surface area allow picophytoplankton to benefit from nutrient competition and to hold a dominant position in the tropical oligotrophic waters of low latitudes. There was a positive correlation between size-fractionated biomass and temperature with pH and a negative correlation between size-fractionated biomass and silicate with phosphate. There was a positive correlation between size-fractionated primary production and temperature and a negative correlation between size-fractionated biomass and salinity with phosphate. Phosphate was an important factor influencing the size structure of phytoplankton. Meanwhile, irradiation and the euphotic layer were more important in regulating the vertical distribution of size-fractionated phytoplankton in the Dongsha natural gas hydrate zone.

This study investigates an environmentally friendly technology that utilizes waste by-products (waste acid and waste alkali liquids) to treat mineral processing wastewater. Chemical precipitation is used to remove silicate from scheelite (CaWO4) cleaning flotation wastewater and the waste by-products are used as a substitute for calcium chloride (CaCl2). A series of laboratory experiments is conducted to explain the removal of silicate and the characterization and formation mechanism of calcium silicate. The results show that silicate removal reaches 90% when the Ca:Si molar ratio exceeds 1.0. The X-ray diffraction (XRD) results confirm the characterization and formation of calcium silicate. The pH is the key factor for silicate removal, and the formation of polysilicic acid with a reduction of pH can effectively improve the silicate removal and reduce the usage of calcium. The economic analysis shows that the treatment costs with waste acid (0.63 $/m3) and waste alkali (1.54 $/m3) are lower than that of calcium chloride (2.38 $/m3). The efficient removal of silicate is confirmed by industrial testing at a plant. The results show that silicate removal reaches 85% in the recycled water from tailings dam.

The research demonstrates an efficient, innovative and environmentally friendly technology which uses one waste (waste acid) to treat another (wastewater) and significantly improves the scheelite roughing recovery by 5% compared with the same periods of previous years in the winter times. A series of modelling exercises and laboratory experiments are conducted to understand and explain the improvement achieved at the plant in Luanchuan. The speciation modelling shows that at high pH, calcium ion hydrolyses to form calcium hydroxide which cannot react with silicate to create calcium silicate and prevent the silicate removal, and thereby affects the scheelite flotation. The experiments of precipitation and sedimentation, FTIR and SEM have confirmed the prediction. Specifically, hydrochloric acid contained in the waste acid reduces pH and decreases the hydrolysis of calcium and formation of calcium hydroxide. The calcium chloride in the waste acid can precipitate silicate as calcium silicate which effectively absorbs fine solid particles in the wastewater and increases their settling velocity. The tailings provide the carrier for the precipitation, increase their settling velocity and compress the sediment bed. At the plant, the new process using the waste acid removes 60–65% of silicate from the recycled water from the tailings dam which is frozen in winter, leading to the inefficient removal of silicate being harmful to the scheelite flotation.

This study presents a highly selective reagent system that utilizes sodium hexametaphosphate (SHMP) to improve the separation of scheelite from calcite and fluorite using an anionic&ndash, nonionic collector. The recoveries of calcite and fluorite decreased to 20% as the SHMP dose exceeded 6 &times, 10&minus, 6 mol/L, whereas that of scheelite remained at 85%. The interaction mechanisms of minerals with SHMP were investigated through equilibrium speciation, Zeta potential, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy analyses. SHMP exists as hydrogen phosphate anion in the aqueous solution with a pH of 7&ndash, 12. Moreover, it may be adsorbed intensively on the positively charged surfaces of calcite and fluorite via electrostatic force or chelation with calcium ion to impede further adsorption of the assembled collector. By comparison, the adsorption of SHMP is feeble on the scheelite surface because of its negative charge. The roughing grade of low-grade scheelite ore is substantially improved from 0.74% to 1.65% compared with that in the contrast test in the absence of SHMP.

The distribution of chlorophyll a (Chl a) and its relationships with physical and chemical parameters in different regions of the Bering Sea were discussed in July 2010. The results showed the seawater column Chl a concentrations were 13.41–553.89 mg/m2 and the average value was 118.15 mg/m2 in the study areas. The horizontal distribution of Chl a varied remarkably from basin to shelf in the Bering Sea. The regional order of Chl a concentrations from low to high was basin, slope, outer shelf, inner shelf, and middle shelf. The vertical distribution of Chl a was grouped mainly from single-peak type in basin, slope, outer shelf, and middle shelf, where the deep Chl a maxima (DCM) layer was observed at 25–50 m, 30–35 m, 36–44 m, and 37–47 m, respectively. The vertical distribution of Chl a mainly had three basic patterns: standard single-peak type, surface maximum type, and bottom maximum type in the inner shelf. The analysis also showed that the transportation of ocean currents may control the distribution of Chl a, and the effects were not simple in the basin of the Bering Sea. There was a positive correlation between Chl a and temperature, but no significant correlation between Chl a and nutrients. The Bering Sea slope was an area deeply influenced by slope current. Silicate was the factor that controlled the distribution of Chl a within parts of the water in the slope. Light intensity was an important environmental factor in controlling seawater column Chl a in the shelf, where Chl a was limited by nitrate rather than phosphate within the upper water. Meanwhile, there was a positive relationship between Chl a and salinity. Algal blooms broke out at Sta. B6 of the southwestern St. Lawrence Island and Stas F6 and F11 in the middle of the Bering Strait.

A selective organic depressant was investigated to promote the separation of scheelite from calcite and fluorite. 1-Hydroxyethylidene-1, 1-diphosphonicacid (HEDP) could efficiently reduce the recoveries of calcite and fluorite to less than 20%, while that of scheelite remained above 85%. The selective interaction mechanism was demonstrated via Zeta potential and X-ray photoelectron spectroscopy (XPS) analyses. The conceivable adsorption models of reagents on mineral surfaces were constructed to explain their adsorption mechanism. HEDP exhibited an excellent ability to selectively depress calcite and fluorite attributed to the intense adsorption on their surfaces, whereas its adsorption on scheelite surface was feeble. The technology feasibility of using HEDP to improve the scheelite flotation performance was verified through laboratory and industrial tests. The roughing grade was dramatically improved from 1.22% to 1.68%, and the product grade was enhanced from 24.66% to 28.26% with a noteworthy improvement of cleaning recovery by 6.93%, which would produce a considerable economic benefit.

An efficiently optimized reagent regime was investigated to improve scheelite heating flotation. The scheelite grade and recovery in the plant were significantly improved by 5% and 6%, respectively, which remarkably augmented the economic profit by $260,000 per month. The interaction mechanisms of sodium sulfide and sodium oleate with scheelite, calcite and fluorite were evaluated by adsorption amount and Fourier transform infrared (FTIR) analyses. Sodium sulfide exhibited an excellent ability to promote the adsorption and desorption of sodium oleate on the scheelite surface and from the calcite and fluorite surfaces, thus facilitating the separation of scheelite from fluorite and calcite.