Effects of process parameters on the comminution capability of high pressure water jet mill     

Longlian Cui  Liqian AnWeili Gong 《International Journal of Mineral Processing》2006

To improve comminution efficiency, the effects of several process parameters on the comminution capability of high pressure water jet mill were investigated. Fractal dimension of particle size distribution, as an index of water jet mill comminution capability, was used for describing the fineness of the comminution product. Nine process parameters including the pump pressure, the mixing tube length and diameter, the coal particle mass flow rate, the diameter of feed material particle, the standoff distance, loading times, hardness of the target and the impact angle were investigated individually. The results obtained from this study provide deeper insight into the high pressure water jet comminution technology and a basis for process parameters optimization. We also show that the fractal dimension of particle size distribution can be used to monitor the comminution capability and estimate the degree of particle comminution.  相似文献   

Study on mechanochemical effect of silica for short grinding period     

Samayamutthirian Palaniandy  Khairun Azizi Mohd AzizliHashim Hussin  Syed Fuad Saiyid Hashim 《International Journal of Mineral Processing》2007

Silica was ground in an oscillating mill at various grinding period to study the mechanochemical effect in fine grinding process. The ground particles exhibited massive size reduction where the volume moment diameter of 5.56 μm was reached within 600 s. Aggregation of fine particles was very pronounced when it was ground for 600 s due to high surface energy. Aggregation of fine particles caused the ground particles to exhibit poly-modal particle size distribution. Line broadening and reduction of diffractogram peak intensity were observed. Amorphization rate up to 16.9% was exhibited by the particle ground for 600 s. Preferential breakage of plane was observed where (101) and (111) was easily distorted compared to (110) and (200). Rapid reduction of crystallite size was observed at early stage of grinding until it reached a plateau at 5 nm at 600 s whilst the change in lattice strain was 0.5%.  相似文献   

Role of feed moisture in high-pressure roll mill comminution     

D.W. Fuerstenau  A.-Z.M. Abouzeid 《International Journal of Mineral Processing》2007

The application of high-pressure roll mills (HPRM) for industrial comminution has been growing, particularly because of its energy efficiency. Many aspects of HPRM comminution have not been fully characterized because the performance of the machine is affected by numerous parameters that still need to be investigated and optimized. The present paper is concerned with the effect of feed moisture on HPRM performance. The comminution of minus 8-mesh dolomite feed at several different moisture levels was conducted with a laboratory HPRM to delineate the effect of feed moisture on product characteristics, specific energy consumption, and such mill operating parameters as applied load, roll gap and roll speed. The results showed definite effects of moisture on these parameters and the product size distribution, most likely because of lubrication of the particles in the compacting bed as they pass through the roll gap.  相似文献   

Use of 234U and 238U isotopes to evaluate contamination of near-surface groundwater with uranium-mill effluent: a case study in south-central Colorado, U.S.A.     

R. A. Zielinski  D. T. Chafin  E. R. Banta  B. J. Szabo 《Environmental Geology》1997,32(2):124-136

The ²³⁴U/²³⁸U alpha activity ratio (AR) was determined in 47 samples of variably uraniferous groundwater from the vicinity of a uranium mill near Cañon City, Colorado. The results illustrate that uranium isotopes can be used to determine the distribution of uranium contamination in groundwater and to indicate processes such as mixing and chemical precipitation that affect uranium concentrations. Highly to moderately contaminated groundwater samples collected from the mill site and land immediately downgradient from the mill site contain more than 100?μg/l of dissolved uranium and typically have AR values in the narrow range of 1.0–1.06. Other samples from the shallow alluvial aquifer farther downgradient from the mill contain 10–100?μg/l uranium and plot along a broad trend of increasing AR (1.06–1.46) with decreasing uranium concentration. The results are consistent with mixing of liquid mill waste (AR≈1.0) with alluvial groundwater of small, but variable, uranium concentrations and AR of 1.3–1.5. In the alluvial aquifer, the spatial distribution of wells with AR values less than 1.3 is consistent with previous estimates of the probable distribution of contamination, based on water chemistry and hydrology. Wells more distant from the area of probable contamination have AR values that are consistently greater than 1.3 and are indicative of little or no contamination. The methodology of this study can be extended usefully to similar sites of uranium mining, milling, or processing provided that local geohydrologic settings promote uranium mobility and that introduced uranium contamination is isotopically distinct from that of local groundwater.  相似文献   

大孔径瓦斯抽放井施工中井内落物打捞     

程志远　迟波王泽山  赵丽华孔令珍 《中国煤炭地质》2008,20(3):65-66

华晋焦煤沙曲矿瓦斯抽放井设计井深405．00m、井径φ700mm,在二次成井中靶后利用自制φ700mm三牙轮组合钻头进行扩孔作业。扩孔作业至150m时,发生三翼牙轮组合钻头掉翼事故,经探查发现井内落物落至井深295m处。根据下落物的重量、形状及井身结构,设计制作了套铣打捞器。自制的套铣打捞工具直径为φ420mm,大小与二开井径较接近,与井壁环空较小,为避免发生二次卡钻事故,采用先扩孔至井中落物,再进行套铣打捞作业的方式施工。打捞采用气举反循环方式,慢转、轻放,经过反复套铣打捞,将二块井中落物打捞出井,事故处理比较成功。  相似文献   

Power aspects of a horizontal ring mill pulverizer under continuous comminution of olivine     

M. Founti  G. Zannis  P. Makris 《International Journal of Mineral Processing》2008

The work presents a theoretical and experimental assessment of the mechanical power absorption by a prototype horizontal ring mill, during the continuous comminution of olivine with feed rates for a wide range of operating conditions. The forces acting on a ring element of a prototype ring mill under continuous operating conditions have been theoretically calculated and it has been experimentally confirmed that they are proportional to the square of the rotational speed. A linear variation of power with feed rate has been established and a functional relationship between consumed power and rotational speed is also proposed. Results demonstrate that there exists a feed rate for which the value of the friction coefficient between the rings and the powdered material is minimized, independently of the rotational speed. It was further found that the product size depends on the absorbed mechanical power and it decreases with increasing power values.  相似文献   

A backbarrier overwash record of intense storms from Brigantine, New Jersey     

Jeffrey P. Donnelly  Jessica Butler  Stuart Roll  Micah Wengren  Thompson Webb  III 《Marine Geology》2004,210(1-4):107-121

Analysis of aerial photographs and historic charts indicates that the barrier beach at Brigantine, NJ has migrated landward 300 to 400 m since 1869, primarily as a result of overwash during hurricanes and winter storms. A series of vibracores from the backbarrier salt marsh reveals a millennial-scale stratigraphic record of overwash deposition. Carbon-14 (C-14) and Cesium-137 (Cs-137) radioisotopic methods were used to date overwash deposits (washovers). The ages of recent washovers are consistent with deposition during intense storms in 1938, 1944, 1950, and 1962. An additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788. Two prehistoric overwash fans were likely deposited by intense storms striking the New Jersey Coast in the 7th to 14th centuries and 6th to 7th centuries A.D. The landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans. The greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period, the hurricane of 1821. The spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments.  相似文献   

Morphodynamics of the barrier-inlet system, west-central Florida     

Richard A. Davis  Jr.  Patrick Barnard 《Marine Geology》2003,200(1-4):77-101

The barrier-inlet system along the Gulf Coast of peninsular Florida has one of the most diverse morphologies of any barrier system in the world. The delicate balance between tidal- and wave-generated processes on this low-energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses. Some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets, closure of inlets due to longshore transport of sediment, and changes in the availability of sediment. Tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area. Human activity has also modified the coast in many ways over the past several decades, beginning with the construction of the first causeways in the 1920s. The various modifications by development have resulted in important morphodynamic changes in the barrier-inlet system. These include hardening the coast on the beach and at inlets, dredging and filling in backbarrier environments, and construction of fill-type causeways connecting the islands to the mainland. Construction of seawalls and jetties has inhibited normal coastal processes. Examples include the downdrift erosion at Blind Pass and Big Sarasota Pass. Construction of fill-type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets, thereby resulting in instability or closure such as Blind Pass and Dunedin Pass. This is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier. Dredging of the Intracoastal Waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets. Impacts of these changes inhibit the barrier/inlet environments from responding to open coast processes.  相似文献   

Erosional and depositional characteristics of regional overwash deposits caused by multiple hurricanes   总被引：7，自引：0，他引：7  

PING WANG  MARK H. HORWITZ† 《Sedimentology》2007,54(3):545-564

Regional-scale washover deposits along the Florida Gulf and Atlantic coasts induced by multiple hurricanes in 2004 and 2005 were studied through coring, trenching, ground-penetrating radar imaging, aerial photography, and prestorm and poststorm beach-profile surveys. Erosional and depositional characteristics in different barrier-island sub-environments, including dune field, interior wetland and back-barrier bay were examined. Over the eroded dune fields, the washover deposits are characterized by an extensive horizontal basal erosional surface truncating the old dune deposits and horizontal to slightly landward-dipping stratification. Over the marshes in the barrier-island interior, the washover deposits are characterized by steep tabular bedding, with no erosion at the bottom. Overwash into the back-barrier bay produced the thickest deposits characterized by steep, prograding sigmoidal bedding. No significant erosional feature was observed at the bottom. Washover deposits within the dense interior mangrove swamp demonstrate both normal and reversed graded bedding. The washover deposits caused by hurricanes Frances (2004) and Jeanne (2004) along the southern Florida Atlantic coast barrier islands are substantially different from those along the northern Florida barrier islands caused by Ivan (2004) and Dennis (2005) in terms of regional extension, erosional features and sedimentary structures. These differences are controlled by different overall barrier-island morphology, vegetation type and density, and sediment properties. The homogeneity of sediment along the northern Florida coast makes distinguishing between washover deposits from Ivan and Dennis difficult. In contrast, along the Atlantic coast barrier islands, the two overwash events, as demonstrated by two phases of graded bedding of the bimodal sediments, are easily distinguishable.  相似文献   

Barrier response to sea level rise and storms          下载免费PDF全文

Chris Houser 《地球表面变化过程与地形》2018,43(11):2481-2483

This commentary brings together, as a Virtual Special Issue, several recent papers in Earth Surface Processes and Landforms that improve our understanding of coastal barrier response to relative sea level rise and a change in the frequency and/or magnitude of storm events. The ability to predict barrier response depends on the ability to quantify the spatial and temporal scales of sediment exchange amongst the nearshore, beach and dune. This exchange controls the height of the dune, which in turn determines the transfer of sediment to the backbarrier through washover and/or blowouts. The papers in this issue provide new insight on beach–dune interaction and the importance of this interaction to long‐term barrier evolution across a range of sites and scales, and how active management can influence this interaction and alter barrier response. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献