Cementitious property of NaAlO2-activated Ge slag as cement supplement

Germanium(Ge),a waste residue leaching from zinc(Zn)smelting process,has potential cementitious properties and could be recycled as a cement supplement activated by chemical reagents.In this work,a test was conducted to determine the hydration properties of Ge slag-cement-based composites with Ge slag(GS)/ordinary Portland cement(PC)contents of 0wt%,5wt%,10wt%,15wt%,20wt%,and 25wt% and water-to-binder ratio(w/b)of 0.4.The activators Ca(OH)2,AlCl3,NaAlO2,and Na2CO3 were mixed under 1wt%,2wt%,3wt%,and 4wt% dosages of GS weight.The composition and microstructure of the hydration products were investigated by the combined approaches of X-ray diffraction(XRD),thermogravimetry-differential scanning calorimetry(TG-DSC),scanning electron microscopy(SEM),and energy-dispersive X-ray spectroscopy(EDS).First,the GS cementitious property is attributed to the high content of CaSO4·2H2O.Second,the activators affected the acceleration performance in the following order:NaAlO2,Na2CO3,AlCl3,and Ca(OH)2.More importantly,the 28-day unconfined compressive strength(UCS)is 45.34 MPa at the optimum formula of 0.6wt% NaAlO2,15wt% GS,and 85wt% PC,which is 9.16% higher than the control.Thus,NaAlO2 is beneficial for the ettringite(AFt)generation,resulting in the C-S-H structure compaction.However,the Zn^2+ residue inhibited the AFt formation,representing an important challenge to the strength growth with curing age.Consequently,the GS could be recycled as a supplement to the cement under the activator NaAlO2.

Influence of Polyaluminum Chloride Residue on the Strength andMicrostructure of Cement-Based Materials

In this paper,cement and dechlorinated Polyaluminum Chloride Residue(PACR)have been used to prepare a net slurry and mortar specimens.Two hydration activity indicators have been used to quantitatively analyze the dechlorinated PACR hydration activity.In particular,the effect of dechlorinated PACR content on the compressive strength of mortar has been assessed by means of compressive strength tests.Moreover,X-ray diffraction(XRD)and scanning electron microscopy(SEM)have been employed to observe the microstructure of the considered hydration products.The following results have been obtained.The 28th day activity index of the dechlorinated PACR is 75%,and therefore it meets the criterion for the use of active admixture.The increase in the content of the dechlorinated PACR tends to reduce the compressive strength of mortar specimens,however,it is beneficial to its later strength growth.When the content is not greater than 10%,the strength remains unchanged,otherwise,it decreases.The PACR does not form a new crystalline phase in the cement slurry,and the dechlorinated PACR remains active until the age of the 28th day.The inclusion of the PACR mainly deteriorates the early strength of the cement slurry,but it promotes the production of hydration products in the cement slurry after the 7th day.

The Micro-Scale Mechanism of Metal Mine Tailings Thickening Concentration Improved by Shearing in Gravity Thickener

Higher concentration is beneficial for the Paste and Thickened Tailings(PTT)operation in metal mine.Partial paste thickeners are produced lower density underflow.Flocculated tailings are intended to form a water entrapped network structure in thickener,which is detrimental to underflow concentration.In this study,the continuous thickening experiment was carried out for ultra-fine tungsten tailings to study the influence of rake shearing on underflow.The micro pores structure and seepage flow in tailings bed before and after shearing are studied by CT and simulation approach to reveal the shearing enhancement mechanism of thickening process.The results shown that,the underflow concentration is increased from 61.4 wt%to 69.6 wt%by rake shearing in a pilot scale thickener,the porosity decreased from 46.48%to 37.46%.The entrapped water discharged from sticks structure more than sphere spaces.In items of seepage,after shearing,the seepage flow channel of tailings underflow is becoming longer,which caused the decreasing average flow rate decreases and absolute permeability.The absolute permeability is negatively correlated with tortuosity.The rake shearing can destroy the flocs structure;change the effective stress to increase the concentration.Higher underflow concentration improves the waste recycling and water recovery rate,especially for arid areas.