Paper Mill Process Research Articles

Зольность тарного картона. Проблемы и пути их решения

This article covers the study of the nature of ash content of containerboard from waste paper, as well as fractional composition of ash. With increasing use of waste paper with white top layer and deterioration of conditions of collecting and storing waste paper at the storing fields, there is an increase in mineral impurities in the incoming waste paper. This fact leads to increased load on cleaning equipment and accelerated wear of working parts of sorters and mills. Ash content includes all mineral impurities without any division into fractions or sources of occurrence. Reducing the total ash content of products becomes quite difficult, because suppliers of cleaning equipment guarantee the efficiency of removing only those mineral contaminants, the size of which is greater than the a certain value (70…100 microns). Standard methods for determining ash content of paper and cardboard do not imply the possibility of determining the fractional composition. To solve this problem, the authors applied a method for determining the fractional composition of granular materials in a certified laboratory. The method of sample preparation for analysis was developed by the authors independently. Based on the results of the research, it was possible to identify the volume of the ash fraction that can be separated by means of cleaning equipment. This volume is mainly quartz sand of various degrees of grinding, and the other part of ash content is the filler, calcium carbonate, which cannot be effectively removed from the technical process due to the small particle size. To determine the content of calcium carbonate, qualitative and quantitative research methods were used - treatment with hydrochloric acid followed by washing and weighing of the resulting sludge. This test methodology and the results of the research work can serve as a basis for the need to install additional or upgrade the existing cleaning equipment. Unfortunately, at present there are no studies concerning abrasive ability of the main filler – calcium carbonate, and its influence on service life of the corrugator. Also, at the moment there are no data concerning critical size of ash particles, which lead to accelerated wear of the rolls. At the same time, determination of critical particle size is important from the point of view of setting up and upgrading of cleaning equipment of the stock preparation department of a typical paper mill processing waste paper raw materials. For citation: Zhirnov D.N., Dernova E.V., Gorazdova V.V., Dulkin D.A. Ash Content of Containerboard. Problems and Solutions. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 5, pp. 184–194. (In Russ.). https://doi.org/10.37482/0536-1036-2023-5-184-194

Insights into the per- and polyfluoroalkyl substances-contaminated paper mill processing discharge: Detection, phytotoxicity, bioaccumulative profiling, and health risk verification

Per- and polyfluoroalkyl substances (PFASs), a new class of contaminants of emerging concern in different water sources and industrial discharges, have been highlighted, mainly ascribed to the high mobility, persistent, and bioaccumulative behaviors. In this work, the analytical detection of PFASs in the paper mill processing discharge (PMPD), physicochemical parameters, tannin and lignin, and phenolic content were carried out. The phytotoxicity evaluation and bioaccumulative profiles of PMPD-assisted irrigation have been conducted using a soilless cultivation system. The cytotoxicity, genotoxicity and human exposure risk were ascertained via in vitro assay on the human hepatocellular carcinoma (HepG2) cell and the estimation of daily intake, respectively. PFASs were quantitatively detected at the mean concentration of 2712.72 ng/L, consisted of mainly perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkane sulfonic acids (PFSAs), perfluoroalkane sulfonamidoacetic acids (FASAAs), perfluoroalkane sulfonamides (FASAs), and fluorotelomer sulfonic acids (FTSAs). Significant reductions of the physical elongation, dry weight, and chlorophylls up to 33.49%, 31.71%, and 52.17% were recorded. Profound increase in the proline (101.81%), hydrogen peroxide (55.56%), superoxide anion (67.86%), lipid peroxidation (43.91%), and protein oxidation (32.31%), and up-regulation of antioxidant enzymes activities have been quantified. Bioaccumulation and translocation of PFASs revealed a concentration-, chain length- and functional group-dependent trend within different plant compartments. PFASs-contaminated PMPD treatments induced dose-dependent cell viability reduction and DNA damage in the HepG2 cell. The findings have highlighted that PMPD could be an underestimated source of PFASs, which represents a sharp threat to plants and public health via the water-food crop-human continuum. Future studies gearing towards the genomic profiling of PFASs in different plant species are suggested.

Recycled paper mill process water pre-treatment using ultrafiltration for water system closure

The use of membranes in integrated water systems has garnered increasing attention in paper mills operating with virgin fibres, with documented closed water loops in industry. However, limited research exists on the performance of ultrafiltration (UF) in mills operating with 100% recycled fibres (RCF) and closed water systems, as these result in the introduction and accumulation of insoluble contaminants in the effluent. This study investigated the effect of transmembrane pressure (TMP) and feed organic load on the flux, types of fouling, and organic separation with UF membranes in a recycled paper mill using 100% RCF. The high feed organic load caused inevitable fouling, limiting the highest achievable flux. However, the TMP could be manipulated to improve on or exacerbate the process performance, within the range that was set as a result of the feed's characteristics. Low TMP (1.35 bar) generated the highest permeability and chemical oxygen demand removal, while higher TMPs produced higher fluxes and recoveries. The process was characterised by high initial fluxes, followed by cake formation, which dominated, and pore blockage. The excess cake formation induced cake filtration. This study shows the potential of UF membranes to be used as pre-treatment in filtering the process water in a recycled paper mill operating with 100% RCF, a critical step forward in implementing an integrated water system, and eventually closing the water loop.

Thermal evaluation of the use of porous ceramic plates on ventilated façades – Part I: Effect of composition and firing temperature on porosity and bending strength

AbstractThe effect of composition and firing temperature on porosity and bending strength of porous ceramic plates for using in ventilated façades were investigated. Two byproducts, basalt and lime mud, were used to obtain porous ceramic plates in accordance with the circular economy concept. Basalt, which is a fine powder‐based byproduct generated from the processing of basaltic rock, was used to replace feldspar as the flux mineral in a ceramic composition. Lime mud, a byproduct of the pulp and paper mill process and containing a high content of calcium carbonate (CaCO3), was incorporated in the ceramic composition to generate pores. The specimens were prepared using three different amounts of lime mud (20, 30, and 40 wt%) and three firing temperatures (900°C, 1000°C, and 1100°C), and their porosity and bending strength were determined. The highest performing specimen (5.1 ± 1.3 MPa bending strength and 42.6 ± 0.5% porosity) was obtained by using 40 wt% of lime mud and a firing temperature of 1100°C with potential for further thermal tests in a ventilated façade in comparison with a commercial porcelain ceramic tile as reference material.

Pulp and paper industry wastewater treatment: use of microbes and their enzymes

AbstractPulp and paper industry is coming under one of the most water polluting industries, and generated wastewater is highly toxic in nature. The paper mill requires huge quantity (~50–60 m3of water to produce one ton of paper) of water, and accordingly huge quantity of chemical contaminated wastewater is discharged. The paper mill effluents have identified 240–250 chemicals in different stages of paper making. Various chemical constituents such as high chemical oxygen demand, biochemical oxygen demand, AOX, chlorinated compounds, color, suspended materials, lignin and their derivatives are released in the wastewater. The present review study is focused on the paper mill processes, wastewater generation and its effective treatment by microorganisms. The biological treatment has been identified as cost-effective and eco-friendly methods for the degradation of xenobiotic compounds for paper mill wastewater. Various studies have been performed so far to investigate the complex nature of wastewater by the application of bacteria, fungi and their enzymes at industrial scale. Therefore, the article discussed the importance of biological method as an effective technique for the degradation of paper mill wastewater.

Ecological risk by heavy metal contents in sediments within the Wei River Basin, China

The Wei River is the largest tributary of the Huang River, which is the second largest river in China. This study aimed to determine pollution and risk assessment of heavy metals, including chromium (Cr), lead (Pb), zinc (Zn), arsenic (As), mercury (Hg), and cadmium (Cd), in 12 selected stations of the Wei River Basin, Northwest China. Results indicated that the pollution and potential risk in Weijiabao are more severe than the other 11 cross sections. The concentrations and potential ecological risk of Pb and Hg and Cr, Pb, Zn, As, and Hg were observed in moderately contaminated and considerable risk levels given industrial wastewater discharge, correspondingly. For the single element, the relative contaminated status and potential risk levels for Cr, Pb, Zn, As, and Hg were Zn > Hg > Cr > Pb > As and Hg > Pb > As > Cr > Zn, respectively. The Cr in sediments may derive from agricultural activities given the utilization of chemical fertilizers, whereas Pb, Zn, and As may derive from industrial wastewater and sewage sludge. Metal melting wastewater in the upper reach and paper mill and textile process wastewater in the middle reach of the Wei River should be disposed of and should satisfy the corresponding criteria of the Integrated Wastewater Discharge Standard (GB8978-2002). Furthermore, a scientific application of chemical fertilizers in the Jing and Beiluo Rivers should be implemented in the reach.

Evaluating Short Paper Fiber as a Soil Amendment for Abandoned Mine Land Reclamation in West Virginia

Maximizing the use of onsite material to create topsoil has the potential to reduce costs for mine reclamation in the eastern United States. This study evaluated the addition of short paper fiber (SPF), a by-product of paper mill processing, to coarse coal refuse (CCR) to aid in vegetation establishment. Vegetation growth in two blends of SPF and CCR (80% CCR with 20% SPF; 60% CCR with 40% SPF) was compared to growth in refuse. Ground cover was monitored weekly, and biomass was measured. The SPF/CCR blends resulted in significantly higher ground cover and biomass than the refuse alone. Therefore, the addition of SPF shows potential to support vegetation establishment in CCR. Ground cover reached the minimum level needed for environmental permit release (70%) for both SPF/CCR blends, but ground cover decreased to below 50% on average by the end of the study. Further study should be completed at a large scale.

An Analysis of the Cost Effectiveness for Energy Efficiency Technology in Thailand Pulp and Paper Industry

Green Energy efficiency is becoming more important because of the resulting cost reduction and image of green society which helps to enhance competitiveness in a globalized green market. Pulp and paper manufacturing is a large-scale industry which is generally regarded as important for national development. The Pulp and Paper industry consumes approximately 2.5% of total industrial energy consumption in Thailand by 44 factories distributed throughout the country. Therefore, energy efficiency improvement can play a significant role in the industry. Investigations of the cost effectiveness of energy efficiency measures and technologies using bottom-up Conservation Supply Curve (CSC) in the pulp and paper mill process are required. This study examines the concept, methodology, and the usefulness of the energy conservation supply curve, and the potential to create the appropriate energy policies to the Thai Pulp and Paper Industry.

Zeta Potential as a Tool to Evaluate the Optimum Performance of a Coagulation-flocculation Process for Wastewater Internal Treatment for Recirculation in the Pulp and Paper Process

The pulp and paper mill process requires large amounts of water. Therefore, the need to reuse water through the application of coagulation-flocculation processes, which is effective in the removal of solids and colloidal particles, has risen. In such processes, zeta potential (ZP) provides important information about the efficiency of the reagents used. The purpose of this study was to develop individual and combined tests of reagents to study turbidity and COD reduction based on ZP in the process of wastewater internal treatment for recirculation in the pulp and paper process. Factorial models were developed to explain the behavior of ZP depending on the different coagulants/flocculants. The statistical analyses showed that ZP had a positive correlation with parameters related to removal (COD and turbidity). It was demonstrated that innovate use of lentil extract (Lens esculenta) applied with aluminum sulfate favored the treatment, consistent with a coagulation-flocculation mechanism. The optimum doses of lentil extract were able to reduce the requirements of aluminum sulfate by almost 29%, providing an alternative strategy for water reuse processes in the pulp and paper industry.

Treatment of a Mixture of Chloromethoxyphenols in Hypochlorite Medium by Electrochemical AOPs as an Alternative for the Remediation of Pulp and Paper Mill Process Waters

Here, 100 mg L−1 of dissolved organic carbon of aromatics including chloromethoxyphenols were prepared by exposition of a mixture of guaiacol, syringol, and vanillin in 200 mM NaClO at pH 3.0 and 25 °C for 14 h and further degraded by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF). Electrolyses were performed with a cell containing either a Pt or boron-doped diamond (BDD) anode and an air-diffusion cathode at constant current density. Oxidants were hydroxyl radicals (•OH) formed at the anode surface from water oxidation and in the bulk from Fenton’s reaction between added Fe2+ and H2O2 generated at the cathode, as well as active chlorine species produced from the anodic oxidation of HClO. Oxychlorine ions like ClO3 − using Pt and ClO3 − + ClO4 − using BDD were detected in the electrolyzed solutions. A poor mineralization was found using the Pt/air-diffusion cell, with increasing relative oxidation ability in the sequence AO-H2O2 < EF < PEF. In contrast, overall mineralization was achieved in all EAOPs using the BDD/air-diffusion cell due to the larger amounts of highly oxidizing •OH generated at BDD. For this latter system, the effect of UVA light, current density, and NaClO and/or Fe2+ concentration on the mineralization rate was examined. Up to 11 chloroderivatives of the parent molecules including four chlorophenols, six chloromethoxyphenols, and one chloromethoxynaphthalene were identified by GC–MS. The removal of these aromatics in AO-H2O2 with Pt or BDD was monitored by UV–vis spectrophotometry, HPLC, and GC–MS.

Automatic Synthesis for the Reachability of Process Systems with a Model Checking Algorithm

This study focuses on the applications of model checking techniques in automatic synthesis for the reachability of process systems. Model checking is an automatic method used to verify if a circuit or a condition, expressed as a concurrent transition system, satisfies a set of properties. The strength of this method lies in its ability to synthesize a feasible sequence with a counterexample and to verify its correctness using temporal logics such as computation tree logic (CTL) simultaneously. These challengeable approaches are implemented in a commercial software package (UPPAAL) using graphical discrete modeling, automata theory, and CTL to automate the synthesis for the reachability of process systems. Three use cases of interest in computer-aided engineering due to the difficulty involved in synthesizing them manually are explored. In the first use case, the optimal operating procedure according to the objective function of a paper mill process is synthesized. In the second use case, a challengeable attempt to optimize supply chain networks is tested. In the third use case, alternative pathways with the desired constraints are found in biochemical networks. The paper also explains how the proposed model checking method can be used efficiently in graphical modeling with automata theory to automatically synthesize process systems counterexamples using CTL by means of the case studies.

Industrial wastewater re-use: closure of water cycle in the main water consuming industries – the example of paper mills

Paper mill, chemistry, textile and food processing industries are high water consumers. Within the framework of the European project Aquafit4Use, the possibility to close the on-site water loop is studied. The aim is to find new technologies or innovative treatment trains to produce water that is ‘fit for use’ in the industrial process; an example of a paper mill is given. Laboratory-scale tests on nine technologies were carried out to determine the best suitable treatment train: anaerobic process (already on site) → aerobic process (already on site) → Flexible Fibre Filter Module → softening → nanofiltration → evapoconcentration or ozonation on nanofiltration (NF) concentrate. This treatment train is currently compared on site at pilot scale to another treatment train including some modifications on the existing on-site biological treatment: anaerobic process → softening → membrane bioreactor → nanofiltration → evapoconcentration or ozonation of NF concentrate.

Influence of Pitch Composition and Wood Substances on the Phase Distribution of Resin and Fatty Acids at Different pH Levels

Pitch emulsions were prepared to mimic the colloidal wood resin system in paper mill process waters. The phase distribution of resin and fatty acids (RFAs) between the colloidal lipophilic droplets (l) and the water phase (w) were determined as pKlw values. The effect of triglyceride to RFA ratio on pKlw values was studied, to determine if seasonal variations in wood extractives influence their phase distribution. The effect of water-soluble hemicelluloses on pKlw values was also determined. The pKlw values of the RFAs were lower in emulsions with a low triglyceride to RFA ratio. Addition of water-soluble galactoglucomannans also lowered the pKlw values of the RFAs.

Evaluation of behavior and fouling potential of wood extractives in ultrafiltration of pulp and paper mill process water

Colloidal extractives particles are potential foulants in pulp and paper mill applications. Characterization of them as foulants is a challenging task because of the complexity of these mill waters. In this study one regenerated cellulose (RC) membrane and two polyethersulphone (PES) membranes were used to study the fouling of extractives in ultrafiltration (UF) of two chemithermomechanical (CTMP) pulp mill process waters. The process waters originated from a pulping process using softwood and a mixture of hardwood and softwood. Extractives were analyzed by extracting them from the membranes and further analyzing them with gas chromatography and by measuring Fourier Transform Infrared (FTIR) spectra for the pure, fouled, and extracted membrane samples. In this study retention of extractives was over 90% even though their molar masses are less than 1kgmol−1. Both dissolved and colloidal extractives fouled the membranes. The fouling behavior was different for the process waters used and it seems that the individual extractive groups had different fouling mechanisms. Mostly fatty and resin acids fouled the membranes, but sterols contributed to the fouling of RC membrane remarkably even though their amount in the process waters used was low.

Sustainable Product Portfolio And Process Design Of The Forest Biorefinery

INTRODUCTION The North American forestry industry has been challenged in recent years by high energy costs, increasing fibre costs, and aging mill assets that have not been adequately modernized [1]. The so-called forest biorefinery (FBR) has emerged as an interesting candidate for reviving the industry. The FBR may use ligno-cellulosic (woody, agricultural) biomass as raw material and implies full utilization of biomass for the production of fibres, chemicals and/or energy, and thus offers an alternative strategy for its utilization. Its design should consider both the retrofit design of pulp and paper mill processes and the product portfolio [2]. There is an apparent complexity in this development, and therefore a rigorous design framework is needed. The concept of sustainability consists of three dimensions: economic, environmental and social. However, design typically emphasizes economic objectives for decision making between process alternatives, and the environmental and social aspects of alternatives are considered as constraints (e.g. [3; 4]). Multi-criteria decision making (MCDM) methods may be used to consider all sustainability dimensions as objectives. METHODOLOGY Design framework Figure 1 shows a design framework that takes into account the design of the product portfolio and biorefinery production process [7]. It consists of a set of process systems engineering (PSE) tools that together cover all aspects of FBR process and portfolio design. In this framework, an MCDM method is used for design decision making based on the analysis results using the PSE tools. MCDM methods raise the awareness of the decision maker(s) about the problem complexity and they can be used to address decision uncertainty.

Masculinization of Eastern Mosquitofish (Gambusia) and Exposure to Pulp and Paper Discharge: Diminished Responses Following Mill Process Modifications

Abstract The abnormal induction of anal fin elongation (masculinization) in female Gambusia was first reported in the 1980s for Florida streams receiving pulp and paper effluents. Although these early reports indicated masculinization responses that were similar to the complete development of a gonopodium (male secondary sex structure), additional evaluations throughout the 1990s demonstrated significant reductions in this response. These historic data suggested that mill process modifications may have been responsible for the reduced masculinization responses. The objective of the current study was to utilize Georgia Pacifics Palatka Mill to monitor a series of mill process modifications and their effects on masculinization responses in Mosquitofish (Gambusia). Gambusia were collected from upstream, discharge, and downstream sites in the Palatka Mill receiving stream (Rice Creek) and masculinization was evaluated. Collections were conducted annually during 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2008, and 2009, before and after a series of modifications which included: conversion to elemental chlorine free bleaching, conversion of secondary treatment to aerobic degradation, reduction of in-mill black liquor losses, addition of condensate stripping, reduction in water usage from 136 to 83 million litres per day (36 to 22 million gallons per day), installation of new brown stock washers, and oxygen delignification. Masculinization responses were evaluated using the anal fin index (ratio or anal fin rays 4 and 6). Reductions in this masculinization response were observed gradually across 1999 through 2009, with an absence of response in female Gambusia during 2004, 2006, and 2008 to 2009. These data indicate that pulp and paper mill upgrades and process modifications have resulted in the elimination of this biological response in Gambusia.

Membrane evaluation for the treatment of acidic clear filtrate

The total effluent load of a paper mill can be significantly decreased by recycling of purified clear filtrate (CF) back to paper-making process. The CF treated with membranes can be reused, for instance, as wire section shower water and in the dilution of chemicals. The main requirements for a membrane in CF treatment are high filtration capacity, high retention of turbidity and low fouling tendency. Previous studies have shown that the regenerated cellulose (RC) ultrafiltration (UF) membrane C30F (current trade name UC030T) is especially suitable for the treatment of paper mill process waters. Every paper-making process is, however, different. Thus, filtration experiments are required in order to find the most optimal membrane for the treatment of a certain process water. In this study the best membrane for the treatment of acidic clear filtrate (ACF) was searched. The performance of the C30F membrane was compared with five UF and three microfiltration (MF) membranes. The results revealed that in addition to the C30F membrane, also some other membranes produced high filtration capacity with ACF (approximately 200 L/(m 2h bar)). All the tested membranes also retained over 90% of turbidity. The extremely hydrophilic C30F membrane had, however, lower fouling tendency compared to the other tested membranes. Therefore, it was concluded that the C30F membranes were the best possible membrane for the ACF treatment.

The Influence of Modified Starch on the Process Water Quality in Papermaking and the Paper Properties

AbstractThe influence of modified (cationic) starch on the process water quality in papermaking and paper properties has been investigated. The experiments were conducted on sulfate hardwood pulp by applying both tap and paper mill process water. When process water is used, the retained amount of starch on fibers decreases, which most probably results from a partial neutralization of the cationic charge on modified starch, thereby reducing its attraction to the anionic groups on a fiber. By adding the modified starch, the turbidity of process water is to some extent reduced, indicating that the suspended organic substances are removed from process water. Due to starch accumulation, the load of process water by organic substances (determined via the TOC analysis) is not reduced, but is rather increased when the modified starch is added. In most cases, the addition of modified starch improved the investigated paper properties. However, these properties varied in correlation with the quality of the used water, despite the fact that the dosage of modified starch remained constant. This demonstrates the influence of process water quality, not only on the paper properties, but also on the efficiency of process chemicals, such as the modified starch, in the papermaking process.

Model-based Predictive Adaptive Control of Pulp and Paper Mill Processes

紙パルププロセスでは，動作が緩慢で変動が大きく，むだ時間が長いプロセスが多く，従来の制御方法の適用が難しかった。従来はカスケード制御，変動モデルパラメータ，あるいはフィードフォワード制御などの従来方式を採用していたが，制御が安定しない為，生産性，製品品質等に影響が出ないように，安全係数を見て操業していた。BrainWaveを商標とするモデルベース予測制御（MPC）は，PID制御が十分に機能しない各プロセスの制御の問題に優れた解決策を提供し，プラント制御を最適化するための理想的なツールと成る。MPCの内部モデルは限りなく実プロセスに近づき，更にプロセス応答中のむだ時間を効率良くモデル化したことにより，将来のプロセス応答の予測を可能として，設定値がすばやく修正・決定されその結果，オーバーシュートの防止などでプロセスを安定させる事ができる。MPCによる安定操業により，動作限界まで操業を改善する事で，省エネ・省人等エネルギーコストの削減，生産性，歩留まり，品質の向上を実現した事例として，ライムキルン制御，ダイジェスタ制御，苛性化設備スレーカ温度／苛性化率制御，パルプドライヤー制御リール白色度コントロールへの導入により，原単位，生産性，品質の向上事例を紹介する。

Antiquarian books as source of environment historical water data

Historical environment considerations are inevitable also for modern environmental analysis. They alone allow evaluation of anthropogenic impact into the environment. To receive information about the historical environment situation in inhabited regions, we approached this task by examining historical well dated and locatable products of the Homo faber. The work introduced here uses books as a source of environment historical data specially for the environmental compartment of water. The paper of historical books, dated by their printing and allocated by their watermark(1) (Wasserzeichensammlung Piccard, Piccard online, Hauptstaatsarchiv Stuttgart, ) is a trap for traces of heavy metals contaminating their production water in historical times. Great amounts of water were brought into contact with the paper pulp in the historical paper mill process. The cellulose of the pulp acts as an ion exchange material for heavy metals, forming a dynamic equilibrium. A well defined pulp production process, starting with used clothes, allows estimation of the concentration of historical heavy metals (Cu(2+), Pb(2+), Zn(2+), Cd(2+)) in the production water (river water). Ancient papers from well dated books are eluted without destruction of their paper and the resulting solution is analysed by ETAAS and inverse stripping voltammetry to determine the historical impact of metals. Afterwards in a flow system the eluted paper spot is equilibrated with different concentrations of heavy metals (Cu(2+), Pb(2+), Zn(2+), Cd(2+)) to plot the adsorption isotherm of that very spot. Both data together allows a calculation of the heavy metal content of the historical river. For different waters of Germany and the Netherlands of the 16th-18th Century the heavy metal load could be estimated. The resulting concentrations were mostly similar to the level of modern surface waters, but in the case of the Dutch waters of the 17th Century, they were e.g. for Pb(2+) significantly higher than modern values.