Sodium Carbonate Dosage Research Articles

Optimization of polyphenol content determination in Perilla leaf by Response Surface Method

In order to improve the utilization value of Perilla leaf polyphenol related food and food additives, and increase the edible added value of Perilla leaf, the polyphenol content of extracts from Perilla leaf was determined. The influence of Folin-Ciocalteu reagent dosage, sodium carbonate dosage, color developing temperature, color developing time and other factors on the determination of polyphenol content were investigated by single factor control variable method, and the determination conditions were optimized by response surface analysis. The experimental results showed that when the determination wavelength was 760 nm, the dosage of Folin-Ciocalteu reagent was 1.0 mL, the dosage of sodium carbonate reagent was 3.2 mL, the color development temperature was 30 °C, and the reaction time was 45 min, the optimal conditions for the determination of polyphenol content showed a good linear relationship with absorbance, and the regression equation was Y=0.0157X-0.0627, R2=0.9991. The stability, precision and reproducibility of the method met the requirements. The average recovery was 95.62% and the relative standard deviation (RSD) was 4.28%. The method was suitable for the determination of polyphenols in Perilla leaves, and the average content of polyphenols in Perilla leaves was 7.439 mg/g, RSD=4.34%. This study can provide data support for the development and researched of Perilla leaf polyphenols and food additives.

Application of Cold Sintering Process for Stabilizing Heavy Metals in Municipal Solid Waste Incineration Fly Ash

Municipal solid waste incineration fly ash (MSWI FA) consists predominantly of compounds comprising elements such as calcium, aluminum, silicon, sodium, and others. Additionally, it encompasses a complex mixture of heavy metals, chlorides, sulfates, organic pollutants, and other constituents. The effective and economically viable treatment of MSWI FA poses a formidable challenge for resource cycling at the current stage. In this research report, we adopt a novel low-temperature sintering method called the “Cold Sintering Process” (CSP) as a means to immobilize heavy metals within the fly ash. By utilizing a Taguchi orthogonal array method, we will adjust five control factors in the CSP, including sintering temperature, uniaxial pressure, sintering time, initial water addition, and sodium carbonate dosage. The leaching of cadmium from the fly ash, as measured by the Toxicity Characteristic Leaching Procedure (TCLP), will serve as the quality indicator of products. Through the application of CSP, MSWI FA was transformed into structurally stable ceramic blocks, and the heavy metals within the blocks were effectively immobilized. The results of the experiments showed that MSWI FA under the conditions of a temperature of 300 °C, uniaxial pressure of 312 MPa, sintering time in 60 min, 25 wt% water addition, and 9 wt% Na2CO3 addition could effectively reduce the leaching of cadmium by 77.71%, lead by 21.14%, zinc by 42.37%, and chromium by 99.99%, as compared to the original MSWI FA TCLP results. The X-ray Diffraction (XRD) results indicate that during the CSP, fly ash forms phases such as calcium silicate, rankinite, hydrogrossular, anorthite, and marilite. These phase transformations are considered beneficial for preventing the leaching of internal heavy metals. Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) results reveal that CSP is advantageous for compacting the overall structure, and EDS results further demonstrate that some of the Pb and Zn are carried out from the interior of the blocks, with uneven distribution on the surface of fly ash particles. The aforementioned experimental results serve as preliminary indications of CSP’s capability to stabilize detrimental components within high-purity fly ash. Future research endeavors may entail the refinement of material proportions, modification of experimental parameters, and other methodologies, thus facilitating potential scalability to industrial applications. Such developments align with the overarching goal of resource utilization.

Extraction of Gallium from Brown Corundum Dust by Roasting—Acid Leaching Process

Brown corundum dust is a solid waste produced during the preparation of brown corundum with bauxite as the raw material. The dust has a relatively high gallium content; therefore, it is of great value to recover the gallium from this kind of dust. In this paper, a range of analysis and characterization methods, including XRD, XRF, SEM-EDS, and EPMA, were used to determine the occurrence of gallium. It was found that gallium was mainly present in the potassium-rich phase, wrapped by amorphous silicate and the corundum phase. Roasting activation followed by an acid leaching process was proposed to extract gallium from brown corundum dust. An investigation was carried out on the effects of roasting temperature, roasting time, and additive dosage on the recovery of gallium and the evolution of the phase composition of the dust. The results show that the roasting activation of sodium carbonate was better than that of calcium oxide. After roasting at 1073 K for 40 min with a sodium carbonate dosage of 0.5 (mass ratio of sodium carbonate to dust), the phase composition changed completely to mainly consist of sodium silicate, sodium aluminosilicate, and potassium aluminosilicate. In that case, around 93% of Ga could be recovered from the roasted dust through H2SO4 (4.6 mol/L) leaching for 90 min. The leaching process was described well by the kinetic equation of k3t = 1/(1 − α)1/3 − 1, with an apparent activation energy of 16.81 kJ/mol, suggesting that the leaching rate was limited by the transfer of leaching agent across the contacting interface of the dust particles.

Preparation and Properties of Organically Modified Na-Montmorillonite.

This study investigates the montmorillonite (MMT) content, rotational viscosity, and colloidal index of sodium montmorillonite (Na-MMT) as a function of the sodium agent dosage, reaction time, reaction temperature, and stirring time. Na-MMT was modified using different octadecyl trimethyl ammonium chloride (OTAC) dosages under optimal sodification conditions. The organically modified MMT products were characterized via infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The results show that the Na-MMT with good properties (i.e., the maximum rotational viscosity and highest Na-MMT content with no decrease in the colloid index) was obtained at a 2.8% sodium carbonate dosage (measured based on the MMT mass), a temperature of 25 °C, and a reaction time of two hours. Upon organic modification of the optimized Na-MMT, OTAC entered the NA-MMT interlayer, and the contact angle was increased from 20.0° to 61.4°, the layer spacing was increased from 1.58 to 2.47 nm, and the thermal stability was conspicuously increased. Thus, MMT and Na-MMT were modified by the OTAC modifier.

Separation and recovery of zinc, lead and iron from electric arc furnace dust by low temperature smelting

Electric arc furnace dust (EAFD), an important secondary resource, is categorized as hazardous solid waste which contains multiple heavy metals such as zinc, lead and chromium. Smelting-Reduction is considered as an effective method to recover metal elements from EAFD. To efficiently separate the zinc, lead, iron and slag from EAFD, a novel and clean process developed to enhance reduction and lower smelting temperature through sodium carbonate was proposed herein. Thermodynamic analysis and laboratory experiments were carried out to determine the feasibility and reliability of this new process. The optimal conditions were determined as temperature of 1450 °C, sodium carbonate dosage of 4%, C/O of 0.8, holding time of 30 min and basicity of 0.8, and the corresponding volatilization of Zn and Pb could be 99.78% and 89.47% respectively; besides, the reduction of iron could reach 98.98%. Simultaneously, the recovery of iron reached 98.62% and the grade of iron amounted to 93.8%. The melting reduction process of zinc, lead and iron could be divided into three stages according to both the experimental results and the thermodynamic analysis. The short process which is characteristic of high efficiency and low energy consumption, aims to provide a clean and sustainable approach to utilize EAFD.

Performance and sustainability overview of sodium carbonate activated slag materials cured at ambient temperature

The production of Portland cement (PC) which is the main binder in conventional cementitious materials contributes about 7% to the world’s anthropogenic carbon dioxide emission. As the demand for PC is expected to increase significantly in the coming years, it is imperative to find other environmentally friendly alternatives. Alkali-activated binders (AABs) obtained by alkali activation of aluminosilicate precursors are viable alternatives for PC as they possess lower embodied carbon and energy compared to PC. However, the conventional activators (i.e. sodium silicate and sodium hydroxide) are corrosive, expensive and have a high environmental footprint. These limitations have resulted in impractical and expensive applications of such binders on a large scale. On the other hand, sodium carbonate, which is less corrosive, cheaper and available naturally in the environment can be used as a sustainable alternative to sodium silicate and sodium hydroxide. In a quest to propel the application of sustainable binders, this study was undertaken to explore the properties of slag activated with sodium carbonate at ambient temperature. The effect of sodium carbonate dosage on the fresh, mechanical and durability properties are discussed. A simplified sustainability assessment of concrete made with different binders was also carried out and the results showed that the sodium carbonate activated slag concretes are a sustainable alternative to PC concrete to achieve a cleaner environment. • Sodium carbonate was used as an activator in alkali-activated slag systems. • Sodium carbonate activated slag can be used as an alternative to Portland cement. • Materials made with sodium carbonate activated slag exhibited good properties. • Sodium carbonate is more eco-friendly compared to sodium silicate/hydroxide.

The role of recycled waste glass incorporation on the carbonation behaviour of sodium carbonate activated slag mortar

This study investigates the influences of recycled waste glass powder (RGP) on the carbonation behaviour of sodium carbonate activated ground granulated blast furnace slag (GGBS) mortars. The effect of activator dosages, types and RGP addition on resistance to carbonation are evaluated. The results indicate a high dosage of sodium carbonate or water glass combination as activator always can enhance the ability of resistance to carbonation. Furthermore, the addition of 30% RGP in the GGBS binder system seems to significantly improve the resistance to carbonation of mortars. The carbonation shrinkage is reduced after RGP incorporation; at the same time, a higher strength performance is observed. The RGP in sodium carbonate activated GGBS blends shows no influence on the species of reaction products. However, after carbonation, the sample containing RGP promotes the formation of nahcolite, while less bound water loss and calcium carbonate formation are identified. A high volume of gel pores (<10 nm) is formed in the RGP sample compared to specimens only containing GGBS. These properties contribute to a better resistance to carbonation for RGP containing sodium carbonate activated GGBS mortars.

Optimization of dyeing parameters of cotton standardized samples for laundry test of dye transfer inhibition program

In order to prevent light-colored clothes from being stained by dyes released from dark clothes during the washing process, some new-type washing machines have developed the dye transfer inhibition washing program. However, there is no certified reference materials for the test of dye transfer inhibition function. To this end, cotton fabric and reactive dyes are used as experimental materials to prepare standardized samples to evaluate the dye transfer inhibition function of washing machines. Firstly, the single factor analysis method is used to analyze the significance of the dyeing parameters including dye dosage, dyeing temperature, sodium sulfate dosage and sodium carbonate dosage. Secondly, a 4-factor 5-level experimental design and theoretical prediction of the best dyeing parameters are successively carried out through central composite design and response surface method. Two evaluation indicators, the dye release amount of the standardized sample of dyed fabric and the color difference value of the standardized sample of white fabric after washing, are proposed as the response values for response surface analysis to search the optimal dying parameters in theory. The optimal dyeing parameters obtained through response surface analysis are that the dosage of dye is 5.63% (owf), the dyeing temperature is 60 °C, the dosage of sodium sulfate is 93.60 g/L, and the dosage of sodium carbonate is 15 g/L. Experimental results indicate that the standardized samples prepared with optimal dyeing parameters can effectively distinguish the dye transfer inhibition function of washing machines.

Optimization of Extraction Technology of Limonene from Pericarp of Citrus wilsonii Tanaka by Response Surface Analysis

On the basis of single factor experiments,response surface methodology was employed to optimize the extraction process of limonene from pericarp of Citrus wilsonii Tanaka. The extraction technology of limonene from mature pericarp of Citrus wilsonii Tanaka was studied by steam distillation. Based on single factor experiments,sodium carbonate was selected as salting-out component,the three factors of liquid-material ratio,salt dosage and extraction time were set as the independent variables,and response surface methodology was used to optimize the extraction process of limonene.The isolated limonene product was identified by GC-MS and IR analysis. Research results showed that the optimum technological parameters for the extraction of limonene were as follows:The ratio of liquid to material was 4.6:1,the dosage of sodium carbonate was 1.05 g,and the extraction time was 63 min. Under these conditions,the theoretical value and validation value of the extraction rate of limonene was 2.75% and 2.76%,respectively,which were very close to each other.The model could well predict the extraction rate of limonene.

Effect of dosage of sodium carbonate on the strength and drying shrinkage of sodium hydroxide based alkali-activated slag paste

This study investigated the properties of alkali-activated slag (AAS) pastes with NaOH and a blend of NaOH and Na2CO3 as the alkaline activator. The effects of five different Na2CO3 to NaOH molar ratios (0:10, 0.9:10, 2.5:10, 5.7:10 and 15:10) and three different Na2O contents (4%, 6% and 8%) in the alkaline activator on the setting time, mechanical performance and drying shrinkage were tested. The water to slag ratio was 0.35 by weight. The results showed that both the Na2CO3 to NaOH molar ratios and Na2O contents are major factors influencing the fresh and hardened pastes. Higher Na2CO3 to NaOH molar ratios yielded a longer setting time and higher compressive strength. The Na2O content of 6% was more sensitive to the properties compared with 4% and 8% Na2O. When the Na2O content was 4%, the drying shrinkage increased as the Na2CO3 to NaOH molar ratio increased; however, when the Na2O content increased to 6% and 8%, the drying shrinkage decreased as the Na2CO3 to NaOH molar ratio increased. The main hydration products were C-S-H(I), hydrotalcite, calcite and gaylussite. There was a strong relationship between the drying shrinkage and pore structures of AAS. Consequently, the Na2CO3 to NaOH molar ratio of 15:10 and Na2O content of 6% can be regarded as the optimum mix proportion.

Binder chemistry of sodium carbonate-activated CFBC fly ash

The use of circulating fluidized bed combustion in coal power plants is dramatically increasing, and the disposal of the resultant ash is a significant environmental concern. The present study investigated the binder chemistry of sodium carbonate-activated CFBC fly ash. Compressive strength tests showed that strength development was relatively faster in samples with 5% sodium carbonate. The main binder gel in samples with and without sodium carbonate was composed of AFt, AFm and C–S–H, while the formation and Al-substitution in C–S–H was enhanced by sodium carbonate-activation. At an excessive dosage of sodium carbonate, the formation of AFt was significantly hindered due to the precipitation of sodium sulfate, and a notable amount of AFm was formed in its place. The results obtained in this study fill a deficit in the understanding of fly ash activated with near-neutral salts, which are used extensively in several industrial applications, including alkali-activated cements.

Improvement of Sodium Leaching Ratio of Ferric Bauxite Sinter after Direct Reduction

The sodium leaching ratio (ηN) of ferric bauxite direct reduction process is much lower than that of ordinary bauxite; thus, the former consumes more sodium than the latter. ηN can be promoted by increasing the dosage of sodium or restricted by increasing the heating temperature and time. However, the restriction effect of heating temperature is 16.67 times larger than that of heating time, and the restriction effect decreases 47.03 times faster when heating temperature increases than that process of heating time. These imply that ηN improves with the increasing sodium carbonate dosage and the decreasing heating temperature.

Effect of the water content of padded cotton fabrics on reactive dye fixation in the pad‐steam process

A series of padded cotton fabrics with various water contents were obtained through vacuum dehydration. The effects of the water content on the fabric temperature variation during steaming, the colour properties, and the dye fixation rate (%F) were investigated. Dye distribution in the dyed cotton fibres was assessed. The influences of steaming time and sodium carbonate concentration on K/S value and %F of the dyed fabrics with low water content were also evaluated. The results indicate that reducing the water content of the padded cotton fabric to around 25.0% prior to steaming was favoured for reactive dyeing. The temperature of the wet fabric rose rapidly, the K/S value and %F were enhanced, and in addition the dye penetration into the dyed cotton fibres was sufficient. However, for padded fabrics with extraordinarily low and high water contents (e.g. 1.4% and 70.9% respectively), both the K/S value and %F were decreased. Furthermore, a white core phenomenon was evident for the fibres of the dyed fabric with a water content of 1.4%. Variation in the L* values was in line with the K/S values as the fabric water content varied. As expected, steaming time and sodium carbonate dosage can also affect reactive dye fixation greatly and should be determined accordingly for dyeing cotton fabric with low water content.

Effect of carbonate minerals on quartz flotation behavior under conditions of reverse anionic flotation of iron ores

Reverse anionic flotation of carbonate-containing iron ores is quite a challenging process. Studies on this ores conducted in many laboratories or beneficiation plants have obtained poor concentrate grades and separation between quartz and iron minerals, even when valuable minerals are adequately liberated. The presence of carbonate minerals, such as siderite, causes a detrimental effect on quartz flotation recovery (froth product) and separation selectivity between quartz and iron minerals. In this work, the effect of carbonate minerals on quartz flotation from iron mineral was investigated using sodium oleate as collector, starch and calcium as regulators. Microflotation, adsorption, PHREEQC calculation, and Fourier transform infrared spectroscopy (FTIR) measurements were conducted in the investigation. Carbonate minerals (i.e., siderite and dolomite) adversely affected the floatability of quartz and separation between quartz and hematite. Starch dosage experiment results clearly showed that the reduction of quartz recovery in the presence of carbonate minerals was mainly related to starch. In addition, mineral dissolution and sodium carbonate dosage experiments evidently exhibited that CO32− dissolved species of carbonate minerals passively affected quartz flotation recovery. By contrast, both starch and CO32− dissolved species of carbonate minerals adversely affected the flotation recovery. FTIR showed that the strong drop-off in quartz recovery in the presence of carbonate minerals was due to the adsorption of CaCO3 precipitations on quartz surfaces and further their interaction with starch molecules. The appearance of CaCO3 precipitations was caused by reaction of Ca2+ from the hydrolysis of CaCl2 and CO32− dissolved species of carbonate minerals. To decrease the passive effect, a potential strategy to improve the flotation performance of iron ores that contain carbonate minerals at strong alkaline pH is suggested to remove carbonate minerals before separation between hematite and quartz.

Restraining Sodium Volatilization in the Ferric Bauxite Direct Reduction System

Direct reduction is an emerging utilization technology of ferric bauxite. However, it requires much more sodium carbonate than ordinary bauxite does. The volatilization is one of the most significant parts of sodium carbonate consumption, as reported in previous studies. Based on the new direct reduction method for utilization of ferric bauxite, this paper has systematically investigated factors including heating temperature, heating time, and sodium carbonate dosage influencing sodium volatilization. For the purpose of reducing sodium volatilization, the Box–Benhken design was employed, and the possibility of separating iron and sodium after direct reduction was also investigated.

Crosslinking of chitosan fiber by a water-soluble diepoxy crosslinker for enhanced acid resistance and its impact on fiber structures and properties

Chitosan fiber for functional textile applications has drawn great attention due to its naturally occurring antibacterial activity, moisture-retaining and no allergenic reaction. However chitosan fiber has the weight loss defect under acidic processing conditions and during peroxide bleaching, which restricts its application and decreases its functionalities. In the present work, chitosan fiber was crosslinked by a water-soluble diepoxy compound with the aim of enhancing its acid resistance. The effects of crosslinking conditions (sodium carbonate dosage, crosslinker dosage and temperature) on the weight loss of crosslinked chitosan fiber in acid solution were studied. Additionally, the effects of crosslinking on the structures, resistance to peroxide bleaching, tensile strength, thermal stability and dye adsorption properties of chitosan fiber were also discussed. The results showed that the crosslinking by the diepoxy crosslinker was able to greatly reduce the weight loss of chitosan fiber in acid solution, and slightly reduce the weight loss during hydrogen peroxide bleaching. Crosslinking treatment slightly improved the thermal stability of chitosan fiber, and had no impact on the crystalline structure and dye adsorptions of chitosan fiber. However, the dry tensile strength of chitosan fiber decreased linearly with increasing diepoxy crosslinker dosage.

两性捕收剂用于四川清平磷矿的正反浮选试验

为了解决四川清平磷矿因含高倍半氧化物而难以富集的问题，采用两性捕收剂SB-116对四川清平磷矿进行了正反浮选试验研究。在原矿品位为22.06%，磨矿细度为−0.074 mm含量91.6%的条件下，采用正反浮选工艺即正浮选一粗联合反浮选一粗一扫中矿顺序返回，正浮选碳酸钠用量为7.0 kg/t，水玻璃用量为1.5 kg/t，捕收剂MXO-135用量为1.2 kg/t，浮选温度为22℃，反浮选为一次粗选一次扫选，粗选硫酸用量为15 kg/t，抑制剂LMX-1用量为0.6 kg/t，两性捕收剂SB-116用量为0.25 kg/t，扫选LMX-1用量为0.3 kg/t，可以得到精矿品位P2O529.81%，产率63.26%，回收率85.49%的选矿指标。 In order to solve the problem that Sichuan Qingping phosphate is difficult to concentrate because of containing high sesquioxide, the flotation tests were conducted with amphoteric collector SB- 116 used in direct-reverse flotation of Sichuan Qingping phosphate. On the condition of ore grade 22.06%, the grinding fineness −0.074 mm 91.6%, the direct-reverse flotation process that a combination of direct flotation with one roughing and reverse flotation with one roughing, one scavenging and middlings returning was conducted. In the direct flotation, the dosage of sodium carbonate was 7.0 kg/t; the dosage of sodium silicate was 1.5 kg/t; the dosage of collector MXO-135 was 1.2 kg/t and flotation temperature was 22˚C. The reverse flotation was one roughing and one scavenging with the dosage of sulfate 15 kg/t, the dosage of inhibitor LMX-1 0.6kg/t, the dosage of amphoteric collector SB-116 0.25 kg/t in roughing and the dosage of LMX-1 0.3 kg/t in scavenging. The beneficiation indexes of concentrate grade P2O5 29.81%, yield 63.26% and recovery rate 85.49% can be obtained.

Development of greener alkali-activated cement: utilisation of sodium carbonate for activating slag and fly ash mixtures

Alkali activated fly ash/slag (AAFS), a newly evolved type of alkali-activated cements (AACs), is here studied with the aim of developing a more sustainable alternative to Portland cement (PC), known for its adverse environmental impact. In this study, sodium carbonate (Na2CO3) was used as the alkali activator for the fly ash (FA)/slag blends. The effects of different factors on the strength, reaction rate, hydration products and microstructure were examined; these factors include the activator dosage, FA/slag ratio, and curing regime. It was found that increasing the Na2CO3 dosage significantly increased the compressive strength. The inclusion of up to 25 wt% fly ash marginally decreased the compressive strength up to 28 days while the inclusion beyond 25 wt% can lead to a remarkable reduction in strength, particularly for water-cured specimens. Sealed curing in general was found to be beneficial to the strength development of AAFS paste especially at a 50/50 ratio of FA/slag. Both the activator dosage and FA/slag ratio were found to have notable influences on reaction rate and reaction products and microstructure. Increasing the activator dosage accelerates the kinetics of the reaction while increasing the FA/slag ratio slows the reaction rates. The main binding phase is C-(N)-A-S-H with varying Ca/Si ratios ranging between 0.6 and 1.0 depending mainly on FA/slag ratio. The results indicated the possibility of production of greener cementing materials by utilizing appropriate ratios of FA/slag, dosage of sodium carbonate, and curing regimes.

Degradation of Aniline Wastewater Using Dielectric Barrier Discharges at Atmospheric Pressure**supported by National Natural Science Foundation of China (No. 51377075), the Natural Science Foundation of Jiangsu Province of China (No. BK20131412), the Environmental Protection Scientific Foundation of Jiangsu Province of China (No. 201004)

Aniline is a toxic water pollutant detected in drinking water and surface water, and this chemical is harmful to both human and aquatic life. A dielectric barrier discharge (DBD) reactor was designed in this study to investigate the treatment of aniline in aqueous solution. Discharge characteristics were assessed by measuring voltage and current waveforms, capturing light emission images, and obtaining optical emission spectra. The effects of several parameters were analyzed, including treatment distance, discharge power, DBD treatment time, initial pH of aniline solutions, and addition of sodium carbonate and hydrogen peroxide to the treatment. Aniline degradation increased with increasing discharge power. Under the same conditions, higher degradation was obtained at a treatment distance of 0 mm than at other treatment distances. At a discharge power of 21.5 W, 84.32% of aniline was removed after 10 min of DBD treatment. Initial pH significantly influenced aniline degradation. Adding a certain dosage of sodium carbonate and hydrogen peroxide to the wastewater can accelerate the degradation rate of aniline. Possible degradation pathways of aniline by DBD plasmas were proposed based on the analytical data of GC/MS and TOC.

Improvement for sulphidation roasting and its application to treat lead smelter slag and zinc recovery

The conventional sulphidation roasting process is usually accompanied by the emission of SO2, leading to serious environmental pollution. This study focuses on the decrease or elimination of the poisonous gas by introducing carbon to the system and its further application to zinc recovery from the lead smelter slag. The effects of temperature, dosage of sodium carbonate, carbon powder and pyrite and time on the sulphidation extent of zinc were studied at a laboratory scale and the sulphidation extent reached 85·62% under the optimum conditions. The results confirmed that the novel improvement for the sulphidation roasting was feasible. Besides, it was found that adding sodium carbonate was favourable for the growth and aggregation of zinc sulphides grains in the slag. Flotation tests indicated that zinc sulphides produced could be separated from the treated slag and the zinc grade increased from 14·07 to 25·12% after one rougher flotation.