title: Effect of chemical and biological degumming on the adsorption of heavy metal by cellulose xanthogenates prepared from Eichhornia crassipes

authors: Deng, Li

subjects: Eichhornia crassipes

abstract: Cellulose xanthogenates, derived from the straw of Eichhornia crassipes, were prepared as adsorbents for heavy metals by CS₂ sulfonation and magnesium substitution after degumming with alkali, self-isolated A₁ strain and pectase, respectively. The effects of three degumming treatments were compared by functional groups analysis, surface morphology and surface element composition and heavy metal (Pb²⁺) adsorption studies. The results demonstrate that bio-degumming treatments by A1 strain and pectase have weaker degumming effects than alkali treatment. However, the surface characteristics of the bio-degumming products, especially the pectase degumming product, are more beneficial to heavy metal adsorption. In comparison to that of the raw plant materials, the Pb²⁺ adsorption performances of the three xanthogenates improved significantly, although no obvious differences being observed among themselves. From an environmental point of view, the two bio-degumming treatments, especially the pectase degumming treatment, are more beneficial to prepare heavy metal adsorbents than the alkali degumming treatment.

text: Effect of chemical and biological degumming on the adsorption of heavy metal by cellulose xanthogenates prepared from Eichhornia crassipes Cellulose xanthogenates, derived from the straw of Eichhornia crassipes, were prepared as adsorbents for heavy metals by CS₂ sulfonation and magnesium substitution after degumming with alkali, self-isolated A₁ strain and pectase, respectively. The effects of three degumming treatments were compared by functional groups analysis, surface morphology and surface element composition and heavy metal (Pb²⁺) adsorption studies. The results demonstrate that bio-degumming treatments by A1 strain and pectase have weaker degumming effects than alkali treatment. However, the surface characteristics of the bio-degumming products, especially the pectase degumming product, are more beneficial to heavy metal adsorption. In comparison to that of the raw plant materials, the Pb²⁺ adsorption performances of the three xanthogenates improved significantly, although no obvious differences being observed among themselves. From an environmental point of view, the two bio-degumming treatments, especially the pectase degumming treatment, are more beneficial to prepare heavy metal adsorbents than the alkali degumming treatment.

year: 2012

title: Development and application of a method for U-Th dating of the Bonney Drift, Taylor Valley, Antarctica

authors: Smith, David W.

abstract: The lacustrine carbonates of the Bonney Drift, Taylor Valley, Antarctica were deposited in lakes proglacial to glaciers advancing through the valley, and now occur as lag and clasts in the glacial drift formed by the glacier. They commonly contain 8 to 25% detritus, including high levels of silica, titanium, iron, manganese, and other elements; making the extraction and purification of uranium and thorium problematic.

A standard U-Th dating process was adapted to deal with the technical problems peculiar to the samples dated. Silica often formed a gel at the head of the U-Th separation column, and was removed using HF. Titanium frequently precipitated out during the conversion of the thorium fraction from a HCl matrix to HNO₃ form (used for further ion exchange purification) causing very low thorium recovery. This was overcome by using much higher volumes during conversion. 

The uranium eluate from the separation column often contained high levels of iron and manganese. These were removed on a small ion exchange column in HNO₃. The resin and wash volumes were adjusted to allow iron and manganese to wash off, but allowing the uranium to be held and eluted subsequently. 

An electrodeposition method was developed to achieve the thin plates necessary for alpha spectroscopy. Silver cathode discs were used in a teflon plating cell, with a stirrer rotating on the spiral planar platinum anode. An NH₄Cl/HCl electrolyte was used, adjusted in pH after sample uptake. 

Of the 62 samples successfully dated, 13 were eliminated for such reasons as low resolution and spectral shift; leaving 17 duplicates, one triplicate and 12 single analyses for further consideration. Samples with low ²³²Th/TIFFS
Th levels were corrected for detrital ²³²Th addition. 

The dates obtained were considered in terms of age, geographic distribution, and uranium isotope ratios and concentrations. δ180 suggested that samples were derived from either Taylor Glacier meltwaters, or possibly Ross Ice Sheet Stage 6 meltwaters, and showed that δ180 values in the meltwaters increased towards the middle of each event. 

Three major events were identified. 
(i) an extensive period of deposition around 240 to 300kA (Stage 9?), This may possibly represent two events, in a lake(s) most likely formed proglacial to an expanded Taylor Glacier. 
(ii) a short period of lacustrine conditions around 175 to 190 kA ago, correlated with either Taylor Glacier expansion at the end of Stage 7, or Ross Ice Sheet thickening at the start of Stage 6. 
(iii) a period of carbonate deposition from 130 to 80 kA( Stage 5), more extensive than that at 175-190 kA. The expanding glacier (Taylor II) then advanced through the carbonates, and those of the earlier events, and redeposited. 

The events interpreted appear to correlate with global interglacials, as suggested by Hendy et al (1979). It seems that during interglacials, the East Antarctic Ice Sheet expands (the absence of a sea ice apron allows increased precipitation). As a result, expansion of the East Antarctic Ice Sheet would be expected as a consequence of greenhouse gas warming, offsetting sea level rises caused by melting of temperate glaciers and ice sheets.

text: Development and application of a method for U-Th dating of the Bonney Drift, Taylor Valley, Antarctica The lacustrine carbonates of the Bonney Drift, Taylor Valley, Antarctica were deposited in lakes proglacial to glaciers advancing through the valley, and now occur as lag and clasts in the glacial drift formed by the glacier. They commonly contain 8 to 25% detritus, including high levels of silica, titanium, iron, manganese, and other elements; making the extraction and purification of uranium and thorium problematic.

A standard U-Th dating process was adapted to deal with the technical problems peculiar to the samples dated. Silica often formed a gel at the head of the U-Th separation column, and was removed using HF. Titanium frequently precipitated out during the conversion of the thorium fraction from a HCl matrix to HNO₃ form (used for further ion exchange purification) causing very low thorium recovery. This was overcome by using much higher volumes during conversion. 

The uranium eluate from the separation column often contained high levels of iron and manganese. These were removed on a small ion exchange column in HNO₃. The resin and wash volumes were adjusted to allow iron and manganese to wash off, but allowing the uranium to be held and eluted subsequently. 

An electrodeposition method was developed to achieve the thin plates necessary for alpha spectroscopy. Silver cathode discs were used in a teflon plating cell, with a stirrer rotating on the spiral planar platinum anode. An NH₄Cl/HCl electrolyte was used, adjusted in pH after sample uptake. 

Of the 62 samples successfully dated, 13 were eliminated for such reasons as low resolution and spectral shift; leaving 17 duplicates, one triplicate and 12 single analyses for further consideration. Samples with low ²³²Th/TIFFS
Th levels were corrected for detrital ²³²Th addition. 

The dates obtained were considered in terms of age, geographic distribution, and uranium isotope ratios and concentrations. δ180 suggested that samples were derived from either Taylor Glacier meltwaters, or possibly Ross Ice Sheet Stage 6 meltwaters, and showed that δ180 values in the meltwaters increased towards the middle of each event. 

Three major events were identified. 
(i) an extensive period of deposition around 240 to 300kA (Stage 9?), This may possibly represent two events, in a lake(s) most likely formed proglacial to an expanded Taylor Glacier. 
(ii) a short period of lacustrine conditions around 175 to 190 kA ago, correlated with either Taylor Glacier expansion at the end of Stage 7, or Ross Ice Sheet thickening at the start of Stage 6. 
(iii) a period of carbonate deposition from 130 to 80 kA( Stage 5), more extensive than that at 175-190 kA. The expanding glacier (Taylor II) then advanced through the carbonates, and those of the earlier events, and redeposited. 

The events interpreted appear to correlate with global interglacials, as suggested by Hendy et al (1979). It seems that during interglacials, the East Antarctic Ice Sheet expands (the absence of a sea ice apron allows increased precipitation). As a result, expansion of the East Antarctic Ice Sheet would be expected as a consequence of greenhouse gas warming, offsetting sea level rises caused by melting of temperate glaciers and ice sheets.

year: 1991

title: Cultural identity and academic achievement among Māori undergraduate university students

authors: Bennett, Simon T.

subjects: Maori

abstract: Cultural identity and academic achievement were investigated among a nonrandom
sample of 72 undergraduate Māori university students studying at Massey
University. Student problems were examined to identify the types of difficulties
most prevalent among this population. The degree to which cultural identity
moderates the relationship between student problems and academic achievement
was then examined. Major findings were that (a) there is a consistent negative
relationship between student problems and academic achievement; and (b) cultural
identity moderates the effect of student problems on academic achievement, in that:
a high degree of problems were associated with decreases in grade point average
among respondents with low cultural identity; while among respondents with high
cultural identity, high levels of student problems had little negative effect on grade
point average. Despite the study having limitations, the findings have important
implications for Māori students, deliverers of tertiary education, tertiary education
providers, and those involved in the development and implementation of tertiary
education policy.

text: Cultural identity and academic achievement among Māori undergraduate university students Cultural identity and academic achievement were investigated among a nonrandom
sample of 72 undergraduate Māori university students studying at Massey
University. Student problems were examined to identify the types of difficulties
most prevalent among this population. The degree to which cultural identity
moderates the relationship between student problems and academic achievement
was then examined. Major findings were that (a) there is a consistent negative
relationship between student problems and academic achievement; and (b) cultural
identity moderates the effect of student problems on academic achievement, in that:
a high degree of problems were associated with decreases in grade point average
among respondents with low cultural identity; while among respondents with high
cultural identity, high levels of student problems had little negative effect on grade
point average. Despite the study having limitations, the findings have important
implications for Māori students, deliverers of tertiary education, tertiary education
providers, and those involved in the development and implementation of tertiary
education policy.

year: 2003